ECN Forum Forums Technical Discussion Electrical Theory and Applications DC on AC rated devices

I know most, if not all, devices used in AC wiring are not rated for DC. What would happen if, say a fuse, switch, lampholder, receptacle, incandescent bulbs, were used on a DC circuit at the same rated voltage (let's not worry about what it would do to appliances). is there an overheating issue? What about using a higher frequency AC (say 600hz instead of 60)
Thanks,
Josh

Switches and fuses (or breakers) rated for AC only should not be used on DC. The problem is that DC is more difficult to interrupt due to the greater tendency to arc. Any wire will have some amount of inductance, and this will cause a voltage spike if a switch or fuse is opened. This voltage spike may be much higher than the nominal voltage and it may be enough to create an arc across the opened switch or fuse.

Lampholders probably will not have a problem on DC, as long as you don't try to remove the lamp with the power on. Incandescent lamps will work fine on DC.

I've never worked with high frequency AC, so I can't answer that part of your question.

That's good enough reason not to use them. I'm trying to incorporate a little bit of 12 or 24V solar/wind power in my house. I've been designing systems for the past 5 years (www.otherpower.com my systems are less crude than theirs, but it's the same basic idea.) I'm just trying to find some type of receptacles/fuses rated for DC. I've found compact fluorescent bulbs for 12VDC with a Medium Edison base. I would never use a NEMA receptacle of any kind on my system just because I don't want to plug the wrong thing in the wrong plug. I am trying to shy away from cigarette lighter plugs.

The possibility or drawing an arc is why switches rated for DC need to be a quick-break type. Back when DC supplies were in use here, DC-rated light switches had a spring-action toggle mechanism, so that no matter how slowly you tried to move the operating handle you'd just reach a certain point, then the spring would snap the contacts right open in one go. Ditto for the main switchgear.

I had an inverter in for repair a few weeks ago, a fairly high-quality true-sinewave unit from a Swiss manufacturer. Yet they'd used a circuit breaker on the 12V input which was a regular domestic type rated for AC only.

Since you have been experimenting for some time, you will be aware of the transient nature of wind/solar, and will probably have incorporated a storage battery(s) - (deep-draw Golf-Buggy type I hope- and do some searching on the net to see how to make these have a long life) - in your design. Why not put a 12vdc-120/240vac inverter at your 12V output- then all 'your' power can use standard ac parts and you can wire everything to US Codes, nice and safe.
(Kept ABSOLUTELY TOTALLY separate to your POCO supply of course!!) I have a UK catalog here now-
330W =US$9O 1000W = US$350- & a LOT cheaper in the US- you lucky buggers! Inverters do burn some power when unloaded, so you do need a 12vdc switch(s) for isolation- and I know just the place- Auto-breakers yard- a key/ignition switch & relay for a car starter motor- one of those mothers will switch 200A! Sounds a good project.
Alan.