48 VDC through a 240 VAC breaker and panel.

[qcroanoke]

I know by code you can't do this unless the panel and breakers are also rated DC.
Got this in a E-mail today.
"We do use the standard Cutler-Hammer BR style panel. 200 A, 120/240V 40 space house panel. Like I said the rating may not be there for DC using a single pole breaker, that's why we use double pole breakers and break both the positive and negative side of the DC circuit.
To the circuit breaker current is current, no matter if it's DC or AC.....
especially in thermo magnetic breakers."

Is this statement correct?
I am asking because I'm running into a brickwall on this.
This is what the customer wants I'm being told. Customer is a POCO and can do as they please.
Is this dangerous?
or is the big deal the fact that the panel is not listed for DC and therefore a NEC violation?

 

[don_resqcapt19]

I think that the Square D QO breakers are rated for 48vdc, but not sure about the Eaton BRs.

 

[Jraef]

Current is current, but DC is harder to break than AC, so the voltage rating is almost always much lower. It is however fairly common for 240V rated breakers to be rated at 48VDC. Just ask or check their data sheets, it proobably provides a DC maximum votlage.

Also be aware that if your DC is grounded on one side, you still can't break the grounded side, which might make it tricky using a panelboard for distribution. What a lot of people do now is use the new IEC style DIN rail mounted breakers and feed them with the combs.

 

[zog]

Nonesense, DC is much harder to interupt than AC, so the AIC rating in a DC application will be much smaller than in an AC application. So how can you know if the breaker is properly applied without knowing the DC AIC rating?

Now for a thermal magnetic breaker, the thermal element reacts to heat produced, which is a factor of power disipated, so the AC RMS and DC values will be very similar and the thermal element will react abou the same to DC as it will to AC. The magnetic element however reacts to magnetic field strength, which is more reflected by peak values, so the magnetic element will react much slower (Or at a higher current level) to DC than it will to AC.

 

[zog]

Dang Jeff, I got a phone call in the middle of my response so you beat me to it

 

[qcroanoke]

Current is current, but DC is harder to break than AC, so the voltage rating is almost always much lower. It is however fairly common for 240V rated breakers to be rated at 48VDC. Just ask or check their data sheets, it proobably provides a DC maximum votlage.

I have checked every data sheet that I have found and have had no luck in getting any ratings other than 120/240 vac.

 

[broadgage]

A rule of thumb is that switches, contactors, relays, breakers and the like, if listed for AC will be fine on DC provided that the voltage is limited to about 10% of the AC voltage.

A breaker listed for 240 volts AC will in practice be fine on 24 volts DC, but I would be a little doubtfull about use on 48 volts DC. Unless the manufacturer says otherwise.

Use of 2 pole circuit breakers might double the effective voltage rating BUT not perhaps in the case of USA type 120/240 volt breakers, since these are probably only designed for 120 volts on each pole.
A single pole breaker might therefore be suited for 12 volts DC and a double pole one for 24 volts DC, not 48 volts DC.

What about use of 277/480 volt breakers ? a double pole one should be fine on 48 volts DC.

It must be remembered that use of AC listed equipment on DC at about 10% of the voltage though fine and safe in practice, is still likely a violation.
Some breakers though normaly used only on AC are in fact listed for DC as well, the DC voltage rating and breaking capacity will be less on DC.