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Message |
Luis (Sundancer)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 1:40 pm: | |
And yet another electrical question. I'm looking at a circuit breaker, its rated for 15 amps at 240 volts. Does that mean 30 amps at 120? Or 7.5 amps at 120 volts? |
FAST FRED
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 2:27 pm: | |
NO , Amps is a volume (like water in a pipe) volts is the measure of pressure .
For 30A at 120V , that's what you by.
FAST FRED |
Luis (Sundancer)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 3:00 pm: | |
I kind of thought it might be 30, but it doesn't hurt to get confirmation. Another question, can these same circuit breakers be used on a DC circuit? Maybe a better question is, should they be okay to use in a DC circuit? Thank you all for your valued input.
Luis |
Ed Jewett (Kristinsgrandpa)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 5:32 pm: | |
Circuit breakers have to be rated for DC before you can use them on DC. You have to check with the manufacturer, maybe their website.
Not every breaker made by a company is DC rated. Square D Homeline (entry level) are not, but Square D QO breakers are |
Dale MC8
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 18, 2005 - 7:10 pm: | |
Luis, I think what Fast Fred ment was if you want 30A for 120, buy a circuit breaker rated at 30A for 120. I think your circuit breaker is only good for 15A, regardless of voltage. FF correct me if I'm wrong.
Dale MC8 |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 19, 2005 - 12:45 am: | |
Fred meant: If you want a 30 amp breaker, buy a 30 amp breaker.
A 15 amp breaker is good for 15 amps at any voltage up to it's rated voltage. The amperage does not change as voltage changes.
So if you're looking to protect a 30 amp circuit, you need to buy a 30 amp breaker and it doesn't matter what the voltage rating is, as long as it's equal to or more than your circuit.
It's probably quite ok to use AC breakers on 12 volts. On higher DC voltages contact arcing will occur but on 12 volts not much will happen to hurt things. The main basic difference between an AC breaker and a DC breaker is that inside the DC one, there is a lot more "stuff" to quench arcs created as the contacts open. Though this is quite necessary on DC circuits over about 40 volts, is is not much of an issue on 12 volts.
The proper way to do things is to use a breaker rated for DC on a DC circuit.
But you may find that AC breakers work fine... try one and see. The worst it can do is not work, the best that can happen is that it will work. Most ac breakers are magnetic actuated and if they trip on 12 volt DC at or about their rated current, they will very likely be fine on 12 volts DC.
To test one, load it with a bunch of headlights or other items that draw a lot of current, and put an ammeter in series. Keep adding more load until either the breaker trips or you exceed it's rating, and you'll know right away if you have a winner....
Otherwise, just go to ebay and search "DC breaker".
Right now there are ten 30 amp ones very cheap
item 7553867233, auction closing in 11 hours
...and there are many many more up for auction, virtually always. It's no biggie to do it right... |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 19, 2005 - 7:56 am: | |
According to UL requirements, AC breakers can be utilized for DC up to 50 volts, even if they have no DC rating stamped on them.
Richard |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 19, 2005 - 6:02 pm: | |
Thinking about my last nights post (two up) I realized it's not a good idea to use headlights as a load to test breakers.
This is because when cold, a tungsten filament is quite a lot less resistance than when it's hot, thus until the headlight is completely lit up, it will draw in the neighborhood of four times its normal running current. It's called "filament inrush current" and is, for example, a hollywood nightmare for gigantic tungsten lights (in the order of 20kw ) where just the act of turning them on kills generators, cables, switches etc due to the massive inrush currents.
Better to use a bunch of heating elements or things that act a lot more like plain resistors as loads, but not light bulbs or your breaker will pop way before it should...
Sorry about the oversight, I should know better- I used to work with those hollywood lights (I even got a technical oscar for coming up with a simple inexpensive system to soften the inrush!) but it was a long day the other day and my brain was on half speed...
Cheers |
Luis (Sundancer)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, October 19, 2005 - 7:43 pm: | |
You are forgiven. I know all about those brain at half speed occurances.
Thanks,
Luis |
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