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General electrical question

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chris414

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Hi everyone

Two questions here... basically I'm wiring some multiplugs to my workbench with a master switch that will turn on/off all power to the bench.

a) I'm taking the power from two wall sockets - ie. one faceplate, two sockets (something like this **broken link removed**). In my area the current limit is 16A - does that mean that each socket can take 16A, or have those two plugs on the wall just been connected to the mains board via the same cable, meaning that they can only take 16A total?

b) I bought a single throw, double pole illuminated switch so that I can switch these two plugs on/off with one switch (this setup assumes that each socket can take 16A, otherwise it would be pointless obviously). The switch has four terminals, but I see now that the LED in the switch only illuminates when their is a potential difference between the two center terminals (here is the product **broken link removed**). Now the only way I can see for getting the light to illuminate when the switch is on is if I put the switch in the neutral line for the one circuit, and the positive line for the other circuit so that there is a potential difference between the terminals. Is it acceptable practice to put a switch in the neutral line only?
 
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Back the truck up. The whole receptical only gets one circuit breaker worth of amps. You are over-complicating it. May I suggest a single pole, single throw switch with a neon bulb and a receptical, all as one assembly? Available at Home Despot and Lowes in the USA. That gets the switch to fit in a standard electrical box and it only uses up half a receptical worth of space.
 
In theory the sockets should be designed to handle 16A each, although I doubt it'll be able to take it for very long without overheating.

The wiring will generally determine the maximum current rating. Make sure the circuit breaker supplying the circuit is sufficient to protect the cable when overloaded.
 
Good point. National Electrical Code demands that the loads be calculated at no more than 80% of the breaker. Your common 49 cent recepticals are rated at 15 amps. You can buy 20 amp recepticals. I didn't mention that b4 because you said "16 amps" so I figured you knew the "law".
 
National Electrical Code demands that the loads be calculated at no more than 80% of the breaker.

In which section of NFPA 70 can I read that limitation, or where the fuse/breaker becomes the limiting factor? I think it's section 340 (I could be wrong on the section...going off memory) that allows protection up to 175% of the load for just one exception to your "rule".
 
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Hi Chris414,

The duplex outlet you show is a standard 120VAC 15A here in the US. It is likely supplied by a #14/2 w/gnd from a 15A breaker or fuse if here in the US by code.

Rather than scabbing power off a wall receptacle to gain power for your workbench, which may or not be a rational or SAFE practice, you have a maximum of two options. First get a licensed electrician to look things over to give you the options that are within the code for where ever you live (US, UK?). Second, you may want to have a separate circuit pulled in for your workbench, done by yourself or the licensed electrician. Yes, it costs more, but a potential fire could cost a lot more, to say nothing of the nuisance of resetting a tripped breaker.

As a side note, the illuminating switch you cite would not pass muster here in the US (or Canada) without a steel mounting plate cut for the footprint and maybe a forgiving inspector. There are other options on the market.
 
Thanks for the replies, it is a lot clearer to me now. MRCecil, what specifically is "wrong" with the switch I referenced? I have used one of those plastic junction boxes you see everywhere to mount the switch in so there are no exposed wires. Perhaps talking about "wiring a workbench" makes it sound more hardcore than it is - all I'm trying to do is mount some multiplugs along my bench (it's a long-ish bench, hence the need for a few multiplugs) at home for working on small hobby projects. I don't have any equipment that will be pulling anywhere in the region of 15A, it's just mainly stuff like an oscilloscope, bench power supply, scroll saw (90W), drill press (450W), soldering iron, glue gun, laptop, etc... ie. no heavy equipment really and only one or two of them would ever be running at the same time.

Since a few have mentioned fire risk etc, I was wondering whether my method of joining wires together is acceptable... all I did was bare the wires, solder them firmly together, wrap each wire tightly with insulation tape, and then wrap all three wires together with more insulation tape for strength.
 
As a side note, the illuminating switch you cite would not pass muster here in the US (or Canada) without a steel mounting plate cut for the footprint and maybe a forgiving inspector. There are other options on the market.
Why, it's UL approved, shorely that's enough?
 
Chris414,

Nothing is inherently wrong with the switch itself. Note that I was speaking to the method of mounting and the application of use. The switch, for which you provided a link, is for panel mounting employing friction-locking tabs. Those tabs are effective only if inserted into a surface whose thickness is within specified limits for the size limits specified for the cut-out up to 0.118". That is why I mentioned the metal box cover. Strength of the plate and its ability to hold the switch in place is a factor given the switch is not mounted to the box directly.

Further, these switches are not approved for general electrical use per UL and CSA. They are classified as a "special purpose component". The CSA certificate for the switch states: "These [listed switches] are Certified only for supply to manufacturers for the assembly, as components, of Certified electrical equipment where the suitability of the combination is determined by CSA International."

Given CSA and ANSI/UL standards are in sync and reciprocally accepted, one can safely assume the UL "Green Book" will have the same definition and limitations for "special purpose component" certified devices. I can't read German, but odds are the VDE approval also classifies that group of switches in the same manner; special purpose. Getting that by an electrical inspector or an insurance company inspector after a fire could be challenging.

Regarding your wire junction method, there is no mechanical bonding holding the wires in place. Wire nuts would be the proper, safest and approved method of making those junctions. They cost pennies each and are quick, easy and safe.

Safety first, last and always is being prudent.
 
I see your point but in my view using a metal plate would make it more dangerous because it would need to be earthed - another connection to potentially fail.

I would say: don't use the switch, if it's going to be a problem with complying with the regulations.
 
Yes, ground bonding is necessary as a given, which would not be a problem as it is code this side of the pond, and a ground wire would be present in every correctly wired box.

And I was trying to lead Chris414 to that conclusion that this was an improper application for that switch. I guess I could have been a bit more to the point, initially.
 
a ground wire would be present in every correctly wired box.
Same here, it's just that double insulated is always better than class 1.
 
One slight clarification. Even though the sockets could do 15A, it's the entire circuit that is the limiting factor, not just the one outlet. Most USA household circuits can only carry 15A to ALL the sockets on the circuit. You can draw 15A from a single socket only as long as none of the other sockets on that circuit are being used.

This is why it was suggested to run a separate circuit for you bench.
 
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