Flex Armored (“MC”) cable or Conduit for power upgrade

[electricalintern]

The current service setup is (2) 200 AMP/208V/3P (two tenant spaces each), but now there’s a need to upgrade the service from the electrical room to the tenant spaces to 400 AMP/208V/3P.

The township electrical inspector and building engineers have approved the drawings.

However, the electrician installed MC cable for the 400 AMP upgraded service in the electrical room rather than the conduit specified in the approved drawings.

The existing electrical room setup only includes galvanized hard conduit.

Is it acceptable to use MC cable for the 400 AMP service, or should it strictly follow the approved drawings showing 2 sets of (4#3/0 + 1#1/0 G in 4" conduit)?

What are the advantages and disadvantages of using MC cable compared to conduit in this scenario?

 

[infinity]

MC cable is perfectly acceptable according to the NEC. The one thing that needs to be checked when paralleling cables is that the EGC is large enough.

 

[electricalintern]

MC cable is perfectly acceptable according to the NEC. The one thing that needs to be checked when paralleling cables is that the EGC is large enough.

So based on Table 250.122, I should specify to use 3 AWG.

 

[tom baker]

The smallest size conductor for parallel use is 1/0. Typically the EGC in cable is undersized.
Curious why electrician deviated from approved plans?

 

[infinity]

So based on Table 250.122, I should specify to use 3 AWG.

Correct. If you look at the standard size EGC in these MC cables (https://assets.southwire.com/ImConv...cr=Armorlite-Type-Feeder-MC-Copper-Conductors) you'll see that #3/0 has a #3 EGC which in your 400 amp installation would work. If you were to parallel say 3 sets for a 600 amp feeder the parallel #3/0's would be good but the #3 EGC would be too small. That's why I mentioned in my previous post that when paralleling with cables you need to be cognizant of the EGC size and may even need to order custom cables with the correct size EGC.

 

[electrofelon]

Sounds code compliant but there could be several issues. Is if this required some sort of review by the ahj, they probably will not be happy with having what was installed be different from the plans. You'll probably need to submit some as-built revisions. The other potential issue is if the plans were part of a contract and the customer did not get what they had wanted or had paid for.

 

[electricalintern]

The smallest size conductor for parallel use is 1/0. Typically the EGC in cable is undersized.
Curious why electrician deviated from approved plans?

They said "value engineering"...Without letting us know about the changes

The smallest size conductor for parallel use is 1/0. Typically the EGC in cable is undersized.
Curious why electrician deviated from approved plans?

Correct. If you look at the standard size EGC in these MC cables (https://assets.southwire.com/ImConv...cr=Armorlite-Type-Feeder-MC-Copper-Conductors) you'll see that #3/0 has a #3 EGC which in your 400 amp installation would work. If you were to parallel say 3 sets for a 600 amp feeder the parallel #3/0's would be good but the #3 EGC would be too small. That's why I mentioned in my previous post that when paralleling with cables you need to be cognizant of the EGC size and may even need to order custom cables with the correct size EGC.

I'm confused, so do I use 1/0 or 3 for 2 parallel runs

The cable sized he used was 2 sets of (4) 250 MCM Alum but he never mentioned what ground size he used

 

[infinity]

I'm confused, so do I use 1/0 or 3 for 2 parallel runs

Post #3.

 

[electricalintern]

Post #4 says "smallest size conductor for parallel use is 1/0"

Hence why I am confused since I would use #3 based on Table 250.122

 

[infinity]

Post #4 says "smallest size conductor for parallel use is 1/0"

Hence why I am confused since I would use #3 based on Table 250.122

That bold above doesn't apply.

310.10(G) Conductors in Parallel.
310.10(G)(1) General.
Aluminum, copper-clad aluminum, or copper conductors for each phase, polarity, neutral, or grounded circuit shall be permitted to be connected in parallel (electrically joined at both ends) only in sizes 1/0 AWG and larger where installed in accordance with 310.10(G)(2) through (G)⁠(6).