CCC conduit fill question

[cbrbamby]

I'm not gonna pretend to be as talented as most posters on this forum, had my journeyman license for almost 2 years now and would like some accurate information I just can't get in my area. So here's the deal. We work for one of the largest fast food chains in the world and a new one is coming up and the inspectors are starting to come down on my boss and his methods after apparently doing it wrong for 40 years. In the new store they have clam grills where the majority of the meats are cooked. 4 grills total and each grill requires a 3 phase 50a feed. We usually pipe out of the MDP into vent appliance which houses the 4 receptacles for the grills and the interlock receptacle. And again for almost 40 years 2 in PVC has been used. They've been busted on number of current carrying conductors already so i can't honestly say I can figure this out myself and I wanna know how and I wanna be able to do it in the future.

Edit: wanna know if 12 # 6 thwn is ok

 

[jusme123]

310.16(2)

 

[LEO2854]

I'm not gonna pretend to be as talented as most posters on this forum, had my journeyman license for almost 2 years now and would like some accurate information I just can't get in my area. So here's the deal. We work for one of the largest fast food chains in the world and a new one is coming up and the inspectors are starting to come down on my boss and his methods after apparently doing it wrong for 40 years. In the new store they have clam grills where the majority of the meats are cooked. 4 grills total and each grill requires a 3 phase 50a feed. We usually pipe out of the MDP into vent appliance which houses the 4 receptacles for the grills and the interlock receptacle. And again for almost 40 years 2 in PVC has been used. They've been busted on number of current carrying conductors already so i can't honestly say I can figure this out myself and I wanna know how and I wanna be able to do it in the future.

Edit: wanna know if 12 # 6 thwn is ok

Look in Informative Annex C Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

 

[infinity]

4 grills total and each grill requires a 3 phase 50a feed

So you have 12 CCC's. 50 amps/50%= 100 amp conductor size with a 50% derating (or 100 amp conductor with 50% derating equals 50 amps).

Now find a 100 amp conductor (if THHN you can use the 90? C ampacity) and see if 12 of them will fit in your raceway.

 

[texie]

I'm not gonna pretend to be as talented as most posters on this forum, had my journeyman license for almost 2 years now and would like some accurate information I just can't get in my area. So here's the deal. We work for one of the largest fast food chains in the world and a new one is coming up and the inspectors are starting to come down on my boss and his methods after apparently doing it wrong for 40 years. In the new store they have clam grills where the majority of the meats are cooked. 4 grills total and each grill requires a 3 phase 50a feed. We usually pipe out of the MDP into vent appliance which houses the 4 receptacles for the grills and the interlock receptacle. And again for almost 40 years 2 in PVC has been used. They've been busted on number of current carrying conductors already so i can't honestly say I can figure this out myself and I wanna know how and I wanna be able to do it in the future.

Edit: wanna know if 12 # 6 thwn is ok

Well, it sounds like you are asking a derating question as opposed to conduit fill. Without looking everything up, it would seem that the 2" is fine on fill but the issue is ampacity. If you have 12 CCC you have to derate to 50%. The ampacity of #6 THHN at 90 degree is 75, so 12 conductors would mean that the ampacity is 37.5 amps. So, yes that is not compliant.
This is a good example of why it is not a good idea to run too many branch circuits in one raceway...better to run multiple smaller raceways.
If I am understanding this correctly, the inspectors are correct.

 

[cbrbamby]

Thank you for prompt replies. Like I said I have no where else to turn but here so I can't point to what I'm reading in my code book and ask if what I'm thinking is correct. I originally looked at table 310.15(b)(2)(a) and I came up with the idea that since my number of ccc's is in the 10-20 column that my adjustment was 50% and I thought I was wrong cus I've never seen 100a conductors on 50a breakers for the grills, ever
and so did someone else so I think it's a matter of what's right vs. what is commonly done. I appreciate the help

 

[qcroanoke]

so I think it's a matter of what's right vs. what is commonly done. I appreciate the help

Yeah, what's commonly done will get you in trouble every time.
I worked in the field for 6 years and derate was never mentioned to me.

 

[kwired]

Depending on actual load of these units, you may be able to use 4 AWG copper. Just because they need a 50 amp circuit doesn't mean the load is 50 amps. 4 AWG THHN/THWN @ 90C is 95 amps, and 50% would be 47.5 amps. We generally size conductors to the load and overcurrent devices to the conductor and are allowed to round up to next higher standard device - until that device is over 800 amps.

Also, 125% full load for continuous loads applies to terminal temp when selecting conductors and not to insulation temp when making adjustments, but they probably are not continuous loads anyway, I doubt the load runs for three hours or more without a thermostat cycling it on/off occasionally.

 

[tim clark]

ccc conduit fill

ccc conduit fill

Ask your local inspector, we may not always see eye to eye with all codes with our inspectors, but a good inspector should direct to the area in the code book to find the info to make the necessary corrections or choses to get the job done. Never be afraid to ask they work for the public and for us and can be very helpful and are not our enemies.

 

[augie47]

I am presently inspecting a new fast food install (the golden arches) . It is obviously not the first rodeo for the electricians. They had two 2" conduits from MDP to terminal strips on a whole section of pre-wired cooking equipment (completed with pre-installed Ansul system). One of the conduits had 12 #6 on 60 amp breakers and a few #12s, the other had even more of both. When I pointed out the problem I got that deer in the headlight look and the "we always" reply.
(The job is also rampant with unsupported boxes and conduits and not a bushing in sight).
I don't doubt these guys have gotten away with the work previously and it, in all honesty, is frightening.

 

[qcroanoke]

I don't doubt these guys have gotten away with the work previously and it, in all honesty, is frightening.

Yes, it is. Them for not knowing and you no doubt will be labeled as that %#@% inspector.


Gus, what ever happened with your truck stop issue?

 

[augie47]

Yes, it is. Them for not knowing and you no doubt will be labeled as that %#@% inspector.


Gus, what ever happened with your truck stop issue?

funny you ask... same location..
The battle continues..... I think the tactic is to wear me down
I've quoted just about every NEC reference I know.

 

[crtemp]

Now find a 100 amp conductor (if THHN you can use the 90? C ampacity) and see if 12 of them will fit in your raceway.

How come you can use the 90 degree column, when the terminals on the circuit breaker say use the 75 degree column?

 

[ActionDave]

How come you can use the 90 degree column, when the terminals on the circuit breaker say use the 75 degree column?

You can't if the final apacity after derating is greater than the 75 degree column but you can use the 90 degree column as a starting point.

 

[augie47]

How come you can use the 90 degree column, when the terminals on the circuit breaker say use the 75 degree column?

To some degree, you look at the actual conductor and the insulation separately. You have to take 110.14 into account when you terminate and make sure you don't load the conductor to the point that you cause a heating problem at the terminations. Then you look at the environment and make sure you don't cause insulation damage by overheating. If you are using a 90? insulation (THHN, etc)_ you can use that rating in regard to insulation damage, but, as ActionDave points out, you are still limited by the termination rating based on the actual conductor size.

 

[Dennis Alwon]

Well put Gus. The wire can handle more than the terminals since the wire is rated 90C and the terminals 75C. So for derating the wire fill does not affect the terminal so the 90C is used for that portion of the run. The weakest link must be used as the final ampacity since we don't want more current, or should we say heat, on the terminals then they can handle.