Good afternoon, First I would like to express my gratitude to Mr. Holt and Mr. Hutchings. Got my Journeyman's

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coqui

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Location
Miami
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Electrician
The electrical Engineer shows in the plans 2-16.0KW heaters and 1- 6.0KW CV boxes.. The CV boxes are located in different Rooms. The 480 3 PH. 20A breaker would trip when more then 1 heater was on-line. He stated that the E.C. made a mistake and the breaker in that slot was supposed to be a 30 Amp. Breakers were changed and called it ok. The AWG is 12 THWN, about 50ft from source. Since each serves a different room and a thermostat per unit noncoincident loads would not apply. I may be wrong, but if I do not ask, I do not learn.. Thank You
 
Congratulations and welcome to the forum.
You won’t learn unless you ask, and look in the code book
Re: heater, 30 amp ckt with 12 AWG?
 
Thank You.. Table 310.15(B)(16) THWN Cu 25A 75C
*Refer to 315.15(B)(3)(a)
** Refer to 240.4(D) 20A
2-16k 19AX2 1-6K 7.2 A =Total 39.2A on a 30 amp breaker with # 12 THWN Cu conductor
What am I missing.. All calculations tell me that it is still going overload conductors and will eventually trip breaker.
Thank you for your time Mr. Baker
 
Good Afternoon: Thank you for your help, since the Hospital is still on TCO, just kicked it back to the G.C. Breakers wee switched but units still remain off-line. I know what is going to happen in a few days when patients start complaining of cold rooms.
 
Congratulations on passing your test. I believe that would warrant further review.
All units listed/ labled as 480 v three phase?
 
Thank You Sir.. Chipping away to my Masters. Yes Sir, they are fed from EQH 480/277 4 Wire.
 
Out of curiosity, what type of disconnects did you use at the units if any.
480/277 system, the circuit it 480v three phase. All units are three phase 480v units?
 
Just trying to understand better. If all three phase then I would say your way overloaded. I would not only review the electrical. I would also review the mechanicals. A lot of time the two do not match on equipment. I have seen it were the electrical showed one thing and mech did another. I have even seen. The mech guys hang wrong units. A quick review of mechanical plans will most likely solve the discrepancy if there is one. If the two or three don't match go to lead or boss. As a rule one of the first things I do is check all ele to mech and specs/ shop drawings if available. It has an impact on pipe run lay out and has a trickle down effect on the system(s) from feeders to wire order disc order etc.
Than an RFI would be in order and a possible change order for you company.
 
Keep, in mind also that most heater loads are considered continuous.
 
That circuit requires a 60a 3 pole breaker if you believe you need to add the 125% for fixed resistive heating elements.
You have 38KW at 480v, 3 phase which equals 45.7 amps x 125% = 57.1 amps, so a 60 amp, 3 pole breaker.
 
Are you sure all 3 units were supposed to be on the same circuit? One 16kw unit would need a 25 amp or 30 amp circuit.
 
There are some unknowns here. Is there a MCA and Max OCPD marked on the unit? It may not be compliant for both boxes to be on the same branch circuit.
 
coqui said:
Thank You Sir.. Chipping away to my Masters. Yes Sir, they are fed from EQH 480/277 4 Wire.
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I note you are from Miami, so I'm guessing you got your Miami-Dade electrical journeyman. I wouldn't bother getting a Miami-Dade master as you are better off to just go for a Florida Unlimited EC. A little more work and difficulty but far more valuable. By the way Mike Holt is by far the best prep for the Florida unlimited as that is turf he knows well.
 
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