I HAVE A CUSTOMER THAT HAS 4 TRUCKS THAT NEED POWER FOR BLOCK HEATERS. THE BLOCK HEATERS ARE RATED AT 1800W @120V. THERE IS 3 #10thhn CU SPARE WIRES LEADING NEXT TO THE SPOT WHERE HE WOULD LIKE TO PARK THE TRUCKS. CAN I LEGALLY INSTALL A 30amp DOUBLE POLE BREAKER ON THE 2 #10'S AND INSTALL 2 DOUBLE DUPLEX 20amp 120V REC WITH HAVING THE TAB SPLIT ON THE RECS.
TRUCK BLOCK HEATERS
- Thread starter gk
- Start date
- Status
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: TRUCK BLOCK HEATERS
30A breaker requires 30A recpt. See 210.21(B)(3)
If the 4 truck block heaters will be on simultaneously, then you have a 60A load @ 120V continuous. You would need at least a 37.5A 240/120V circuit, which I would terminate onto a panelboard for distribution to the four 20A dedicated branch circuits for each of the four trucks.
[ November 08, 2004, 11:58 AM: Message edited by: ron ]
30A breaker requires 30A recpt. See 210.21(B)(3)
If the 4 truck block heaters will be on simultaneously, then you have a 60A load @ 120V continuous. You would need at least a 37.5A 240/120V circuit, which I would terminate onto a panelboard for distribution to the four 20A dedicated branch circuits for each of the four trucks.
[ November 08, 2004, 11:58 AM: Message edited by: ron ]
Re: TRUCK BLOCK HEATERS
IDEALLY 4 20amp CKTS IS THE WAY TO GO HOWEVER; LIKE EVERYONE ANYMORE THE BUDGET IS TIGHT AND I WAS JUST TRYING TO FIND A WAY TO USE THE SPARES ALREADY TO THAT LOACATION. THOUGHT ABOUT TRYING TO PULL NEW CKTS THROUGH EXISTING CONDUIT BUT IT IS FULL, EVEN IF I WAS TO REPLACE THE #10'S. THE ONLY WAY TO UPGRADE IS INSTALL NEW CONDUIT ABOUT 150' UNDERGROUND TO THE LOCATION WHERE HE WANTS TO PARK THE TRUCKS. THANKS FOR YOUR GUYS INPUT! STILL ACCEPTING IDEAS!!!!
IDEALLY 4 20amp CKTS IS THE WAY TO GO HOWEVER; LIKE EVERYONE ANYMORE THE BUDGET IS TIGHT AND I WAS JUST TRYING TO FIND A WAY TO USE THE SPARES ALREADY TO THAT LOACATION. THOUGHT ABOUT TRYING TO PULL NEW CKTS THROUGH EXISTING CONDUIT BUT IT IS FULL, EVEN IF I WAS TO REPLACE THE #10'S. THE ONLY WAY TO UPGRADE IS INSTALL NEW CONDUIT ABOUT 150' UNDERGROUND TO THE LOCATION WHERE HE WANTS TO PARK THE TRUCKS. THANKS FOR YOUR GUYS INPUT! STILL ACCEPTING IDEAS!!!!
Re: TRUCK BLOCK HEATERS
Okay, then try using the (3) #10's as opposite hots & a "neutral" from a 30/2 pole feeder bkr. to a little load center with some 20/1 pole branch ckts. to feed however many recepts. you need.
Worst case, if all of the heaters happen to draw large currents simultaneously for long periods, then you trip the 30/2 feeder bkr.
Whether the potential tripping would present a problem or not depends. Like Ron said, NEC requires at least a 37.5A ckt. for 1-PH 3-W.
Okay, then try using the (3) #10's as opposite hots & a "neutral" from a 30/2 pole feeder bkr. to a little load center with some 20/1 pole branch ckts. to feed however many recepts. you need.
Worst case, if all of the heaters happen to draw large currents simultaneously for long periods, then you trip the 30/2 feeder bkr.
Whether the potential tripping would present a problem or not depends. Like Ron said, NEC requires at least a 37.5A ckt. for 1-PH 3-W.
B
bthielen
Guest
Re: TRUCK BLOCK HEATERS
Since the 20A recepatacle is not able to accept anything higher than a 20A plug, it would seem reasonable to expect the end device load would not exceed 20A and the circuit itself, which is sized for 30A, is still protected.
Naturally, an incorrect plug could be wired to the heaters or whatever but the OCPD is not intended to protect the end device, only the circuit. Otherwise, we would have to insall an OCPD for each outlet.
Bob
I'm sure I remember this discussion before but, why not? We can use 15A receptacles on 20A branch circuits. For example, I've seen many SA circuits wired this way.
Since the 20A recepatacle is not able to accept anything higher than a 20A plug, it would seem reasonable to expect the end device load would not exceed 20A and the circuit itself, which is sized for 30A, is still protected.
Naturally, an incorrect plug could be wired to the heaters or whatever but the OCPD is not intended to protect the end device, only the circuit. Otherwise, we would have to insall an OCPD for each outlet.
Bob
Re: TRUCK BLOCK HEATERS
bthielen,
There are many smaller loads throughout electrical technology that are limited to 20A ckts. Among the devices limited to 20A ckts. are 15A & 20A duplexes, fluorescent lamps, etc.
Art. 210, as well as various national publications are clear on this. I would consider this as a given. I do not have time to look-up & list all the rules right now, maybe others do.
Yes, you can use 15A duplex recepts. on 20A ckts.
bthielen,
There are many smaller loads throughout electrical technology that are limited to 20A ckts. Among the devices limited to 20A ckts. are 15A & 20A duplexes, fluorescent lamps, etc.
Art. 210, as well as various national publications are clear on this. I would consider this as a given. I do not have time to look-up & list all the rules right now, maybe others do.
Yes, you can use 15A duplex recepts. on 20A ckts.
- Status