What does this mean? (Electrical question)

[Pandasaurus]

This is probably a stupid question, but I'm going to ask it anyways, so I don't burn my house down or anything. I have a device which has a sticker on it that says "Caution: May contain double pole/neutral fusing."

What does this mean/is it important for the purposes of plugging it in to a standard US 110v outlet? Device in question has a normal 3-prong plug, 100-240VAC power supply. I couldn't find an explanation via Google.

 

[Raizinman]

It sounds like it was written or translated poorly, especially with the word 'may'. Well, does it or doesn't it? Either way, the way I understand this is that normally when something is fused, it is fused on the + side, not the neutral or - side. To my understanding this means that the neutral side is also fused. You tend to find products like this that are used in a bathroom or near water to give an extra measure to prevent shock. The reason for the caution is that should the fuse blow, you need to also look on the neutral - side to reset or replace the fuse.

 

[pcgeek11]

Sorry but AC Alternating Current Circuits ( US household wiring ) does not have a positive or negative lead. That only applies to DC Direct Current Circuits.

AC Circuits have a hot lead black, a neutral lead white and a ground lead bare copper. The neutral and ground are bonded together in the service breaker panel.

I agree it sounds like they fused both the hot lead ( black ) and the neutral lead ( white ).

 

[Mark R]

AC circuits don't have a "polarity" in the true sense of the word (+ or -). However, they are asymmetrical in that they (usually) have a "neutral" and one or more "live" (also called "phase" or "hot") wires.

The neutral wire is connected to ground by the power company, usually at their nearest transformer or power pole.

The livewire(s) carry a high voltage compared to ground. To complete a circuit, you connect a load between liveand neutral.

Because neutral is connected to ground by the power company, it is a low-risk wire. If you touch a bare neutral wire, you are unlikely to be shocked.

However, live wires are high-risk, you may be shocked or electrocuted by contact with a bare phase wire, because by contacting ground you complete an electrical circuit.

It is normal practice to put a switch in the live wire. This way, when you switch something (e.g. a light) off, there is no high voltage present at the appliance. So, if you turn a light off at the switch, if the switch is in the live wire, if you accidentally poke the light socket with your finger you shouldn't get a shock.

If the switch went in the neutral, then the light socket would stay connected to "live" and if you poked it with your finger you may be shocked.

For similar reasons, fuses should always go on the live side. Take a PC which is made of metal. The metal is connected to ground. If a live wire comes loose inside and touches the metal case, then the fuse in the live wire will blow, disconnecting the live wire and preventing the PC case from staying at a dangerous voltage.

The risk with "double fused" items, is that it is possible for only 1 fuse to blow, and 1 to stay active. If the neutral fuse blows, the item will stop working and act like it has no power - but internally, it may be still connected to live, and still be capable of giving a shock if touched.

Sometimes you have to use double fusing if you have a power-lead which can be inserted "upside down", because only a fuse in the live wire will provide protection against a short-circuit fault. If either wire could be live, then both need fusing.

 

[inachu]

Black is power.
White is called common.
Green is ground.
----------------------------The above is for AC USA wiring.

Some homes do have some wiring issues such as FLOATING GROUND.

Its been over 20 years since my electrical trade school days but from what the OP says I think that is what it means...... floating ground.

Best way to see your situation is to buy one of those home depot $7 polarity plugin testers for wall outlets and it will quickly tell you if it has any problems.


Neutral also known as GROUND in my years of work I have never seen it wired to a fuse in either residential or any industrial commercial building. #weird.

 

[Mark R]

Neutral also known as GROUND in my years of work I have never seen it wired to a fuse in either residential or any industrial commercial building. #weird.

Double (Live + Neutral) fusing is not common.

It's only generally used for essential or safety-critical equipment, where there is a risk of incorrect "polarity" connection (e.g. in areas where power plugs can be inserted into a receptacle either way up).

The idea is that if you only have a fuse in "live", but the appliance shorts out while the power cable is connected in reverse polarity, then the fuse is not in the fault circuit - so the upstream breaker must trip to clear the fault. If you have critical equipment on that circuit, then that is bad.

This is commonly done for medical equipment - so if the IV pump shorts out, you don't want it tripping the circuit breaker and knocking out the ventilator. So, medical equipment is double fused, so that if there is an internal short, even if the wiring is wrong, the internal fuse will blow and keep the power to the rest of the equipment on the circuit on.

 

[Pandasaurus]

Thanks guys. So, basically, I'll be fine as long as I don't touch it if a fuse blows? Am I understanding what you're saying?

 

[Paperdoc]

I think what's going on is: this device was designed and built to work on a variety of power supply systems - note that it is spec'd for an input from 120 to 240 VAC. In many European countries it would be fitted with the plug for appropriate local outlets and run on 240 V. Here in North America it comes with what we call a "standard 3-prong plug" and connects to a 120 V supply, and works. BUT because it is possible to connect its two input lines to two Hot lines from 240VAC supply, they have placed fuses in BOTH input lines. (As it happens, on a North American 120 VAC supply, one of those fuses would be in the Neutral line.) This does mean that, if it quits working because one internal fuse blew out, it is possible that the other line with the non-blown fuse is the Hot line, so internal components are still "live". So the proper action in that case is NOT to rely on the blown internal fuse for protection. In the event of failure it MUST be disconnected from the power source before attempting internal repairs or fuse replacement.

The device is fully safe to use here. The caution is for your information if you attempt to work on its innards, including fuse replacement.

 

[MikeD090]

Im reading a lot of technical replies here and actually I am confused in the end. If this statement is found on an A/C to D/C power supply for a stereo boombox, what is the practical meaning here in the United States? ""Caution: May contain double pole/neutral fusing.""

What is the caution I must take? I ask because im curious and at the same time I would like to use this power supply with another electrical item I have that takes the same power specifications and plug and Im afraid to use this power supply since I don't understand the caution at the end of the day.

Thanks!

 

[Paperdoc]

To repeat, the warning is to make sure you understand that, if a fuse "blows" the unit may NOT be safe to work on while still plugged in. Do NOT rely on a blown fuse in this unit to guarantee it is "dead" electrically. It should be completely unplugged from the wall before opening it or attempting to service it.

Yes, it is safe to use in any normal manner.

 

[MrDudeMan]

To repeat, the warning is to make sure you understand that, if a fuse "blows" the unit may NOT be safe to work on while still plugged in. Do NOT rely on a blown fuse in this unit to guarantee it is "dead" electrically. It should be completely unplugged from the wall before opening it or attempting to service it.

Yes, it is safe to use in any normal manner.

The single sentence summary is as follows: fuses protect devices, not users. If a fuse blows and the device has more than a hot-only fuse, unplug it before you mess with it.