Single pole 40A and 50A breakers??

Status
Not open for further replies.
J

jeff48356

Senior Member
Location
Livonia, Michigan
I almost bought a bunch of Square-D 40A breakers on eBay. I was just about to click the Buy Now button when I noticed they were HOM140 (single pole) rather than HOM240 (double-pole, which are next to impossible to find). But my question is, what on earth would single-pole 40A and 50A breakers be used for? I can't think of anything that uses that much current that wouldn't be a 240V circuit, so those would be completely useless to me. In fact, I can't even think of any single-pole 30A circuits other than camper/RV outlets.
 
Some are used in lighting panels for group lighting. The groups, or banks, are fed from a 2 or 3-pole breaker and the single pole controls lights within the group/bank.
 
I have used them on 120v power conditioners and UPS systems.
 
jeff48356 said:
OK, but would those motors ever be used in a residential setting (which is what Homeline is designed for)? If not, then I could see Square-D making those breakers for their QO panels, but not Homeline.
Click to expand...
They probably don't sell all that many of them. A 40 A unit is about 3 or 4 times the price of a 15 or 20 A unit.
 
We use them, single pole 40s and 50s, to feed I/O power to large PLC panels. A small panel inside the PLC enclosure provides branch circuits for inputs, outputs, processor power, panel lighting and receptacles. They didn't want the 240 in the panels to avoid the possibility of a line to line fault.
 
GoldDigger said:
Well, a handle tie would not provide common trip. Would that still be OK for a single no-neutral 240V load? It would be OK for an MWBC.

Sent from my Pixel 4a using Tapatalk
Click to expand...
240.15(B)(2) & (3) would permit them for single and three phase line to line 240 volt loads with handle ties
 
petersonra said:
Where did you hear that?
Click to expand...
I think arcs aren't sustainable at 120 Volts, and the incident energy level for a 120V arc flash would be less than 1.2 calories and thus would not require arc flash PPE. NFPA 70E Annex D gives methods for calculating incident energy levels, and the most common and preferred method is IEEE 1584-2018 and this standard is applicable for 208-15kV 3-phase systems with bolted fault currents of 2000 amps minimum.
 
mayanees said:
I think arcs aren't sustainable at 120 Volts, and the incident energy level for a 120V arc flash would be less than 1.2 calories and thus would not require arc flash PPE. NFPA 70E Annex D gives methods for calculating incident energy levels, and the most common and preferred method is IEEE 1584-2018 and this standard is applicable for 208-15kV 3-phase systems with bolted fault currents of 2000 amps minimum.
Click to expand...
You mentioned 3 phase 208 systems in your response, but 240-120 systems are single phase.
 
petersonra said:
You mentioned 3 phase 208 systems in your response, but 240-120 systems are single phase.
Click to expand...
Yes, because IEEE 1584 is only for three-phase systems. There are ways to do single-phase calcs, but 70E doesn't recognize those methods or 120V single-phase arc flash incidents.
 
I've seen 40A 1P used for "blade server" racks in data centers (a blade server is a smallish computer used to make up a larger system). One 40A feed from the panelboard to a rack, then there is a "PDU" (Power Distribution Unit) on the side of the rack that splits that into two 20A circuits (each with their own CB) and a couple of strings of 15A receptacles for the power supplies of the blade servers to plug into.


Why don't they just use a 20A 2 pole feed? Because this is what it looks like installed, and anything they can do to reduce the number of cables helps.
article-2219188-158CA78F000005DC-369_964x641.jpg
 
Status
Not open for further replies.
Top