| Author | Message | ||
| Douglas Tappan (Dougthebonifiedbusnut)
Registered Member Username: Dougthebonifiedbusnut Post Number: 126 Registered: 10-2004 Posted From: 24.62.45.179  Rating: N/A |
Hey George or Sean or any other of you lectrical guys. I am assuming, you would never out AC threw a DC switch , but is it o.k. to run DC threw an AC switch?. I ask because I am going to use comb. AC and DC lights at every location and would like to have matching switches. Thanks in advance guys. | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1053 Registered: 8-2006 Posted From: 99.184.9.29 Rating: N/A |
Doug, I don't know why not, DC would jump contacts easier than AC, but 12 VDC will be no problem to a 120 VAC switch. G | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 1113 Registered: 1-2003 Posted From: 67.142.130.22  Rating: N/A |
Technically, switches should carry a DC rating to be used on DC. However, there is really no code requirement when under 30 volts, nominal. Additionally, most 120-VAC switches (which you will generally find are actually rated up to 250-VAC) also have DC ratings, which are simply not stamped on the part. If you call the manufacturer (e.g. Leviton, Eagle, etc.) they can often give you the DC rating for the part. All that said, I would take special caution for high-current applications. While using a standard, 15-amp, 120-VAC light switch to switch up to 15 amps of DC lights is probably not going to be a problem, using a 100-amp AC-only rated switch to switch 100 amps of DC (such as a battery disconnect) could be a real problem. This is because DC will arc in such an application, whereas 120-VAC will not. The arcing, in addition to being a hazard in its own right, will cause carbon deposits on the contacts, which will add resistance and ultimately lead to overheating, which can be dangerous. For this reason I would stick to low-current applications only. -Sean http://OurOdyssey.BlogSpot.com | ||
| Tim Hoskinson (Tdh37514151)
Registered Member Username: Tdh37514151 Post Number: 264 Registered: 9-2004 Posted From: 98.28.100.32  Rating: N/A |
AC and DC currents will both arc when connecting and disconnecting across a load. The AC current however has a cooling time during the transition from one current direction to the other. At this time for a brief moment no current flows. This reduces arc energy at the same given voltage for AC verses DC. Switch manufactures rate the switches with this in mind. That said Sean gives very good advice if the DC current you expect to provide across the switch is considerably less than the AC rating you will have no problems. Best of luck. Tim | ||
| Jim Wilke (Jim Bob) (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 513 Registered: 2-2001 Posted From: 65.15.106.226 Rating: N/A |
If your connected DC load is high, you can use a relay to handle the actual load and use the switch to activate the relay. The little cube relays are excellent for the application. A three pole 30 amp DC rated cube relay is continuous duty rated and can be had for $5 or so. Bonus us if the contacts ever fail, you can replace it in a minute. | ||
| John MC9 (John_mc9)
Registered Member Username: John_mc9 Post Number: 1164 Registered: 7-2006 Posted From: 74.162.78.3  Rating: N/A |
Re: "I am going to use comb. AC and DC lights at every location and would like to have matching switches." Of course Doug, if you're talking about both switches in the same box, or side-by-side...... It'll be dandy for you to have both AC and DC wired into the same outlet boxes and into switches that are exactly the same.... And -your- memory is probably just fine.... But what about anyone else that might have to work on your system without you around? Are they going to know that not everything in that box is 12vdc? Will there be any possibility that there will be a cross-connect made in error inside one of those boxes during a period where there is no AC current available..? Crap happens, and having both 12vdc and 120vac in what will appear to be "just any other normal switch box" is just asking for a problem. I'd keep 'em separate and keep 'em marked! | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 1114 Registered: 1-2003 Posted From: 67.142.130.14 Rating: N/A |
John makes a good point; I have been assuming here that when you wrote "matching switches" you meant "matching, but in separate boxes." 120 (and higher) VAC must never be co-mingled with low-voltage (below 30 volts nominal) circuits in the same boxes, conduits, raceways, or panels. This rules out using multi-gang boxes, or, worse, those multi-switch devices that occupy a single-gang box. I recommend that you additionally use a different type of wire or at least different colors for low-voltage wiring than for 120-VAC. -Sean http://OurOdyssey.BlogSpot.com | ||
| Douglas Tappan (Dougthebonifiedbusnut)
Registered Member Username: Dougthebonifiedbusnut Post Number: 127 Registered: 10-2004 Posted From: 24.62.45.179 Rating: N/A |
Thanks Guys, You are "The Best and Brightest"you have a good point Geo but the DC side will be #d while the AC side will not and I will anotate that on my diagrams.And yes Sean the DC will only be 12vdc nothing bigger. And thank you Tim, I'm only using this stuff for lighting. |