How common is an 8volt drop in household wiring?

[JohnCU]

I was ironing earlier and I noticed that when the iron was coming on and off (like, it turns on to heat up then heats back up every minute or two) there was a noticable difference in the fan that I had plugged in.

I plugged in my multimeter and watched it hover between 118 and 119 and then when the iron turned on the heating element (1100W~ish) the voltage dropped to 110.

I don't know very much about householding wiring (they really should give us a practical electricity class) but I'm pretty sure that an 8 volt drop is substantial.

I assume this is due to the resistance/sizing of the wiring, which makes me wonder if the apartment I'm living has appropriately sized wiring...

 

[BrownTown]

well thats a pretty big current draw. I know at my parents house there are several appliances (hair dryer at least, and i cant remember the others), which casue the lights on the same circuit to dim considerably when they turn on (likely due to magnetization inrush currents). I don't think its too big a deal, although you have to thing if you are losing 8V from a 10 amp current draw then you are putting out 80W into your walls, I doubt thats enough to start a fire or anything, but still its wasted $$$.

Also, to my understanding the nominal voltage is 120V at the transformer and 115V at the socket, so 5V drop is assumed. With a 1kW draw I'd think a 8V drop is not to unreasonable, but then again I'm no expert in the field.

 

[Mark R]

That level of voltage drop is excessive.

It's worth trying to identify whether it is due to the particular circuit that your iron is on, or due to the power company's wiring. You should repeat the test with the voltmeter connected to another outlet which is fed from a seperate breaker on the panel. If the meter is still reading signficant voltage drops when connected to a totally different circuit, it suggests a problem in the mains supply.

In general, electrical codes say it's acceptable for the voltage on the same circuit to drop by up to 5V (that's when the circuit is loaded to its max). The voltage at the panel (and therefore other circuits) should drop be considerably less than this.

If the problem is in the circuit wiring, then it needs to be upgraded - as it will be providing less voltage to your appliances (reducing performance), and may well be at risk of overheating, and if you're using that circuit for PCs then it will actually be increasing your power bill.

 

[bobsmith1492]

Let's see; I'll assume the iron has a PF=1 (just a heating element; not too inductive, hopefully).

For the iron:
P = IV -> I = P/V; under load, IL = 1100/110 = 10A.

For the wiring:
R = V/I; Rwire = 8/10 = 0.8 ohms.

That would be for the entire circuit (both hot and neutral lines and transformer impedance.) Standard house wiring is 14AWG; a typical value from here
http://www.powerstream.com/Wire_Size.htm

is 2.525 ohms/ 1000 ft. Assuming 0.1 ohms output impedance of the mains transformer, (0.7ohms)(1000ft/2.525ohms) = 277 feet of wiring.

I suppose that sounds a bit excessive to me; how big is your apartment? If it consists of a row of apartments, maybe the power entry point is at the opposite end of the building? If your apartment complex is anywhere near 277*0.7(curving wires factor)/2(go and return) = 97 feet, then it makes perfect sense.

Also, the iron power factor would have the same effect as the 0.7 distance fudge factor.

EDIT: Whoa, that got borked...

 

[Mark R]

Originally posted by: bobsmith1492

is 2.525 ohms/ 1000 ft. Assuming 0.1 ohms output impedance of the mains transformer, (0.7ohms)(1000ft/2.525ohms) = 277 feet of wiring.

I suppose that sounds a bit excessive to me; how big is your apartment? If it consists of a row of apartments, maybe the power entry point is at the opposite end of the building? If your apartment complex is anywhere near 277*0.7(curving wires factor)/2(go and return) = 97 feet, then it makes perfect sense.

I would seriously hope the wires bringing power to his actual apartment are bigger than 14 AWG. In fact, I'd be very surprised if the bulk of the run was smaller than 3 AWG.

 

[bobsmith1492]

Originally posted by: Mark R

Originally posted by: bobsmith1492

is 2.525 ohms/ 1000 ft. Assuming 0.1 ohms output impedance of the mains transformer, (0.7ohms)(1000ft/2.525ohms) = 277 feet of wiring.

I suppose that sounds a bit excessive to me; how big is your apartment? If it consists of a row of apartments, maybe the power entry point is at the opposite end of the building? If your apartment complex is anywhere near 277*0.7(curving wires factor)/2(go and return) = 97 feet, then it makes perfect sense.

I would seriously hope the wires bringing power to his actual apartment are bigger than 14 AWG. In fact, I'd be very surprised if the bulk of the run was smaller than 3 AWG.

I was thinking about the wires from the breaker box to his actual outlet - maybe the breakers are all at one end of the complex... eh, maybe not.

 

[tekmerion]

evenin' guys,

JohnCU,

I would go to the main breaker(fuse) panel and check the voltage drop for the circuit in question - while the iron is heating. Then, find an outlet off a circuit breaker that is fed from the other leg of the 120/240 split-phase service and measure it's voltage too - again, while the iron is heating.

If the voltage goes down by 8V on the iron's, AND up by 8V on the other leg you may have a faulty neutral connection somewhere between the distribution tranformer on the street (or in your apartment building) and your panel ... or in your panel. This is known as "Neutral Swing". It is always present to some degree or another, due to the small but finite resistance of the neutral wiring, but not usually by +/- 8 volts. CALL THE LDC NOW!!! Faulty neutrals can cause blown TV's, fires, etc., ... BAD. This would be confirmed by the lights getting simultaneously brighter in half the apartment and dimmer in the other half.

otoh, If the voltage only drops on the circuit for the iron but stays relatively constant on the other leg, then follow advice from previous replies.

If there is no voltage drop at the panel, then you have an internal problem.

If the drop also occurs at the panel AND you have your own separate energy meter for your apartment, you need to call your LDC for futher diagnostics. (LDC = Local Dist. Company; or PUC ... Public Utility Company; ... the Electric Co. ... etc., you get the idea.)

Our LDC gives free initial troubleshooting for such problems in order to determine whether the problem is ours (ie: up to the meter outside the residence) or yours (ie: between the meter and the panel or inside the residence) your LDC should too.

If your apartment building is "bulk-metered" and you don't have a separate energy meter, then you need to call the landlord or building super and have them check it out.

If I have just confused the living daylights out of you - welcome to my nightmare.

In any case, feel free to email me as I do this for a living.

Cheers,

 

[Paperdoc]

You are thinking of improper wiring in your building. Not impossible, but not likely, either, because MOST buildings were build to meet a regulatory code and inspected to be sure. However, we must recognize that rules are broken sometimes.

Almost ALL domestic cirsuits are wired with 14AWG wires suitable for 15 amps max load with very little voltage drop over any "normal" cable run length from breaker panel to outlet. From the supply transformer outside to the breaker panel is a different cable, of course, for much higher total loads. The 8 v drop you see is not normal. The most common cause of that is there is one or more poor connections in the cable run you are plugged into. And the quickest way to check that, as others said, is to repeat your voltage measurements back at the breaker panel where the line starts as it comes out of the specific breaker for that circuit. If there is no voltage sag there, that indicates the problem is somewhere is the cable run for that circuit. If the voltage sags there also, then the problem is ahead of that. Could be either in the breaker itself, or in the supply cables coming from the outside. Checking for voltage sag at the point where the supply cable connects to the main breaker panel bus will tell you that one. That would give you a good clue whether the electical supply company or the building owner should be fixing the problem. Of course, if you don't feel confident doing this kind of probing in the electrical system, follow the suggestions from tekmerion and have the electrical utility people do a preliminary problem-isolation check as he said.

If the voltage sag is absent at the breaker panel, then you MIGHT be able to narrow the search along the specific circuit. First you need to know which outlets and lights are on it. Then you run your voltmeter tests at each outlet in turn, looking for a change from no voltage sag to 8 v sag. If there is a particular problem like a bad connection, it will be between the zero-sag and 8 v-sag points. It would be comforting to fix this problem. IF it is one poor connection in a box somewhere, 80W of heat trapped in it can raise the temperature quite a bit. And then, what happens if the bad connection continues to get worse and generate even more heat?

Of course, you MIGHT find that the sag does not show a step change down the circuit, but simply a smoothly increasing measured sag as you progress along the line. Then you just have to assume it is a matter of heavy load on a long line, stop worrying and put up with the behavior.

 

[DrPizza]

Almost ALL domestic cirsuits are wired with 14AWG wires suitable for 15 amps max load

Unless I'm mistaken, the national electrical code requires a 20 amp circuit to the bathroom, at least two 20 amp circuits to the kitchen, and a 20 amp circuit to the laundry room. This requires 12AWG wires, not 14AWG.

Personally, I prefer to use all 12AWG, and 20 amp circuits, rather than 15 amp circuits.

 

[bobsmith1492]

Originally posted by: DrPizza

Almost ALL domestic cirsuits are wired with 14AWG wires suitable for 15 amps max load

Unless I'm mistaken, the national electrical code requires a 20 amp circuit to the bathroom, at least two 20 amp circuits to the kitchen, and a 20 amp circuit to the laundry room. This requires 12AWG wires, not 14AWG.

Personally, I prefer to use all 12AWG, and 20 amp circuits, rather than 15 amp circuits.

Of course, you're assuming all buildings are brand new... every circuit in my parents' house is 15 amp except the basement (which was done just a few years ago) and the house is only 40 years old or so.

 

[DrPizza]

Originally posted by: bobsmith1492

Originally posted by: DrPizza

Almost ALL domestic cirsuits are wired with 14AWG wires suitable for 15 amps max load

Unless I'm mistaken, the national electrical code requires a 20 amp circuit to the bathroom, at least two 20 amp circuits to the kitchen, and a 20 amp circuit to the laundry room. This requires 12AWG wires, not 14AWG.

Personally, I prefer to use all 12AWG, and 20 amp circuits, rather than 15 amp circuits.

Of course, you're assuming all buildings are brand new... every circuit in my parents' house is 15 amp except the basement (which was done just a few years ago) and the house is only 40 years old or so.

Nope, I wasn't assuming anything. Since it was phrased as "almost ALL" with an emphasis on all, I just thought I'd point that out. Many people update the wiring when remodeling, especially kitchens. While 14 AWG makes up the majority, I doubt it's more than 80%, which certainly wouldn't qualify as "almost ALL."

 

[JohnCU]

I'll update in 2 weeks with more data when I get back to the apartment, thanks for the replies!

 

[Paperdoc]

In the area I come from, a 20A circuit MUST have three features: a 20 amp breaker, 12AWG copper wire, and a different outlet blade pattern. The reson is that end-use devices (e.g., a toaster) must be built to stand up to a certain maximum current without hazard. This MAY include a small fuse to limit the current, as in a VCR machine with a hidden fuse inside, or it may be designed to rely entirely on the main circuit fuse or breaker for protection. In the latter case, that means it must be designed to draw up to 15 amps from the outlet and not cause a problem. But if such a device is plugged into a circuit that will be happy to supply 20 amps continuously (and a bit more on surge) it could be running over its design safety factors and over-heat (for example, a pistol-grip hair dryer). To prevent that, a 20A circuit must have a different blade pattern on the outlet so that appliances that were designed to handle up to 15 amps only cannot plug in.

Now, that's not to say you could not use 12AWG wiring in 15A circuits. Especially for long cable runs that is a good idea. It just costs a little more, so many builders don't do that. However, if you put a 20A breaker at the head of the circuit, in my area you then MUST install the different outlets everywhere in the circuit.

Regarding heavier supplies to some parts of the house, my area requires in the kitchen at least three "split duplex" 15A circuits - two min on the counter, and one min near the table. A "split duplex" receptacle looks like a normal 2-outlet unit. But the feed to it is two separate 15A 120V lines from separate breakers (usually off of opposite phases of the supply) and a common neutral. With this you have at each receptacle two independent 15A outlets, and on each line there is only ONE outlet. That way you cannot overload each circuit because all your appliances with 15A plug configuations can only draw up to 15A, and only one can be plugged into each circuit.

I'm sure one of the things we are all running into here is that electrical codes differ from one jurisdiction to another. If you are trying to install something, it is vital you find out exactly what is required. And if you are trying to troubleshoot something (the start of this thread), you might need to know come code requirements in order to understand the system. For that matter, sometimes you are examining a system installed before the more recent code updates!

 

[dkozloski]

Originally posted by: Paperdoc
In the area I come from, a 20A circuit MUST have three features: a 20 amp breaker, 12AWG copper wire, and a different outlet blade pattern. The reson is that end-use devices (e.g., a toaster) must be built to stand up to a certain maximum current without hazard. This MAY include a small fuse to limit the current, as in a VCR machine with a hidden fuse inside, or it may be designed to rely entirely on the main circuit fuse or breaker for protection. In the latter case, that means it must be designed to draw up to 15 amps from the outlet and not cause a problem. But if such a device is plugged into a circuit that will be happy to supply 20 amps continuously (and a bit more on surge) it could be running over its design safety factors and over-heat (for example, a pistol-grip hair dryer). To prevent that, a 20A circuit must have a different blade pattern on the outlet so that appliances that were designed to handle up to 15 amps only cannot plug in.

Now, that's not to say you could not use 12AWG wiring in 15A circuits. Especially for long cable runs that is a good idea. It just costs a little more, so many builders don't do that. However, if you put a 20A breaker at the head of the circuit, in my area you then MUST install the different outlets everywhere in the circuit.

Regarding heavier supplies to some parts of the house, my area requires in the kitchen at least three "split duplex" 15A circuits - two min on the counter, and one min near the table. A "split duplex" receptacle looks like a normal 2-outlet unit. But the feed to it is two separate 15A 120V lines from separate breakers (usually off of opposite phases of the supply) and a common neutral. With this you have at each receptacle two independent 15A outlets, and on each line there is only ONE outlet. That way you cannot overload each circuit because all your appliances with 15A plug configuations can only draw up to 15A, and only one can be plugged into each circuit.

I'm sure one of the things we are all running into here is that electrical codes differ from one jurisdiction to another. If you are trying to install something, it is vital you find out exactly what is required. And if you are trying to troubleshoot something (the start of this thread), you might need to know come code requirements in order to understand the system. For that matter, sometimes you are examining a system installed before the more recent code updates!

Some of this stuff puts you in direct violation of the National Electrical Code. Where are you. Some foreigh country?

 

[Paperdoc]

This was based on expereience in Ontario, Canada. And let me correct one thing about the split duplex receptacles. I said the two lines are "usually off opposite phases...". In fact they MUST be from opposite phases so that the common neutral line carries only the net difference in current. Plus, when this is done, the fuse or breaker system for this dual circuit MUST be such that BOTH hot lines are turned off at the same time, so the entire cucuit is dead when turned off. For a fuse system, the fuse holder is a dual-fuse pullout. For a breaker system, one uses a (tied) dual breaker, of course.

The actual cable for this split duplex receptacle is a 14/3 one (for 15 amp circuits). That is, there are two hot leads (black and red) from the opposite power supply sides, one neutral white lead, and a bare copper bonding / ground lead in the cable. Since these receptacles are intended to supply individual high-power appliances, you are not allowed to make branch connections and put multiple receptacles on the line. The cable must go from the breaker box to ONE split duplex receptacle only.

On the receptacle itself, most are built with pairs of screws each for hot and neutral lines, and bridging pieces on each between the upper and lower halves of the double outlet. For a "normal" receptacle you leave it that way and wire one hot (black) and one neutral (white) to the two sides, following proper rules of which blade must be hot. But for a split duplex on the HOT side you break away the connecting bridge and wire the two hots (black and red) separately to the hot sides of the two outlet sockets, using the two separate screws. The bridge on the common neutral side stays in place. Of course, there's also the ground lead to hook up.

Does that still appear to violate the National Electrical Code in some way?

 

[dkozloski]

Originally posted by: Paperdoc
This was based on expereience in Ontario, Canada. And let me correct one thing about the split duplex receptacles. I said the two lines are "usually off opposite phases...". In fact they MUST be from opposite phases so that the common neutral line carries only the net difference in current. Plus, when this is done, the fuse or breaker system for this dual circuit MUST be such that BOTH hot lines are turned off at the same time, so the entire cucuit is dead when turned off. For a fuse system, the fuse holder is a dual-fuse pullout. For a breaker system, one uses a (tied) dual breaker, of course.

The actual cable for this split duplex receptacle is a 14/3 one (for 15 amp circuits). That is, there are two hot leads (black and red) from the opposite power supply sides, one neutral white lead, and a bare copper bonding / ground lead in the cable. Since these receptacles are intended to supply individual high-power appliances, you are not allowed to make branch connections and put multiple receptacles on the line. The cable must go from the breaker box to ONE split duplex receptacle only.

On the receptacle itself, most are built with pairs of screws each for hot and neutral lines, and bridging pieces on each between the upper and lower halves of the double outlet. For a "normal" receptacle you leave it that way and wire one hot (black) and one neutral (white) to the two sides, following proper rules of which blade must be hot. But for a split duplex on the HOT side you break away the connecting bridge and wire the two hots (black and red) separately to the hot sides of the two outlet sockets, using the two separate screws. The bridge on the common neutral side stays in place. Of course, there's also the ground lead to hook up.

Does that still appear to violate the National Electrical Code in some way?

The U.S. National Electrical Code says there must be at least two 20A outlets and at least #12 AWG on the kitchen counters and one 20A near the table. Depending on proximity to the sink area they must also be GFI protected. 15A and #14AWG in any form won't cut it. They have to be 20A rated outlets but conventional blade pattern. 20A outlets have provisions for horizontal as well as vertical blades but much stronger contact pressure. My kitchen outlets are all 20A and all are GFI protected. Dr. Pizza had it nailed in an earlier post. It seems to me that having a polarized to grounded plug adapter in your posession in Canada is a worse offense than having narcotics. Is that true?

 

[bobsmith1492]

Originally posted by: dkozloski

Originally posted by: Paperdoc
This was based on expereience in Ontario, Canada. And let me correct one thing about the split duplex receptacles. I said the two lines are "usually off opposite phases...". In fact they MUST be from opposite phases so that the common neutral line carries only the net difference in current. Plus, when this is done, the fuse or breaker system for this dual circuit MUST be such that BOTH hot lines are turned off at the same time, so the entire cucuit is dead when turned off. For a fuse system, the fuse holder is a dual-fuse pullout. For a breaker system, one uses a (tied) dual breaker, of course.

The actual cable for this split duplex receptacle is a 14/3 one (for 15 amp circuits). That is, there are two hot leads (black and red) from the opposite power supply sides, one neutral white lead, and a bare copper bonding / ground lead in the cable. Since these receptacles are intended to supply individual high-power appliances, you are not allowed to make branch connections and put multiple receptacles on the line. The cable must go from the breaker box to ONE split duplex receptacle only.

On the receptacle itself, most are built with pairs of screws each for hot and neutral lines, and bridging pieces on each between the upper and lower halves of the double outlet. For a "normal" receptacle you leave it that way and wire one hot (black) and one neutral (white) to the two sides, following proper rules of which blade must be hot. But for a split duplex on the HOT side you break away the connecting bridge and wire the two hots (black and red) separately to the hot sides of the two outlet sockets, using the two separate screws. The bridge on the common neutral side stays in place. Of course, there's also the ground lead to hook up.

Does that still appear to violate the National Electrical Code in some way?

The U.S. National Electrical Code says there must be at least two 20A outlets and at least #12 AWG on the kitchen counters and one 20A near the table. Depending on proximity to the sink area they must also be GFI protected. 15A and #14AWG in any form won't cut it. They have to be 20A rated outlets but conventional blade pattern. 20A outlets have provisions for horizontal as well as vertical blades but much stronger contact pressure. My kitchen outlets are all 20A and all are GFI protected. Dr. Pizza had it nailed in an earlier post. It seems to me that having a polarized to grounded plug adapter in your posession in Canada is a worse offense than having narcotics. Is that true?

Heh, I'm glad it's not here (US); I use anti-ground-pin plugs all the time while running an oscilloscope.

 

[Paperdoc]

Interesting difference in those 15A vs 20A requirements. I certainly have seen the designs with dual horizontal / vertical blade slots. As far as I know they are not encouraged in Ontario, for the reasoning outlined. Likewise, I know that GFI protection IS required there in all bathroom outlets and some other places, but I cannot remember about kitchen rules. Makes a lot of sense - it's just been enough years since I did this that I am not fully up to speed on current rules. By the way, in the USA where the 20A receptacles are required, is that ONE 20 A circuit supplying both outlets in a box, or is it two separate 20A circuits like the split duplex system I outlined?

As far as the adapter goes, I presume you mean those things that allow you to plug a 3-prong into a 2-blade outlet with a separate ground lead you are SUPPOSED TO attach to a good ground. I have one, almost never use it. I am not sure how severe the authorities look on these, but I know you'd be in for a huge reprimand at least if an electrical inspector saw them in use. Of course, the problem is they oftern don't get connected properly. And even when the user makes the effor to ground to the cover plate screw, too often that box in the wall never had a ground to it, anyway. So it is useless and the poor user does not even know!

I can appreaciate, though, bobsmith's reason to use on certain electronic test equipment where ground loops can cause havoc with the signals you're trying to examine!

 

[bobsmith1492]

Yeah, due to the lack of those, someone in my power systems' lab basically connected the output of a variac (0-208VAC) through the scope ground clip straight to ground. Something smoked.... 😛 People just don't take the time to look at the big picture when they're hooking stuff up.

 

[dkozloski]

Originally posted by: Paperdoc
Interesting difference in those 15A vs 20A requirements. I certainly have seen the designs with dual horizontal / vertical blade slots. As far as I know they are not encouraged in Ontario, for the reasoning outlined. Likewise, I know that GFI protection IS required there in all bathroom outlets and some other places, but I cannot remember about kitchen rules. Makes a lot of sense - it's just been enough years since I did this that I am not fully up to speed on current rules. By the way, in the USA where the 20A receptacles are required, is that ONE 20 A circuit supplying both outlets in a box, or is it two separate 20A circuits like the split duplex system I outlined?

As far as the adapter goes, I presume you mean those things that allow you to plug a 3-prong into a 2-blade outlet with a separate ground lead you are SUPPOSED TO attach to a good ground. I have one, almost never use it. I am not sure how severe the authorities look on these, but I know you'd be in for a huge reprimand at least if an electrical inspector saw them in use. Of course, the problem is they oftern don't get connected properly. And even when the user makes the effor to ground to the cover plate screw, too often that box in the wall never had a ground to it, anyway. So it is useless and the poor user does not even know!

I can appreaciate, though, bobsmith's reason to use on certain electronic test equipment where ground loops can cause havoc with the signals you're trying to examine!

One circuit can supply both outlets in one box. The reason I ask about the adaptor is that some come with a printed warning tag attached about being prohibited in Canada.