parallel conductors, seperate panels

[electrofelon]

Pretty sure I am right about this but wanted to double check. I have a 400 amp service with single 400 amp main. From there I have parallel 4/0 AL all in the same pipe - emt and then rigid - to 2 200 amp panels. Each conductor set lands in its own panel. The conduit is the EGC, the panels are in the same building as the service, and the 200's are main breaker although I cant see that that would effect anything. Code violation right? Dont have my book handy but parallel conductors must be joined at each end, and these cant be considered two feeders because they are supplied by the same ocpd. Right? Because the panels are main breakers and not MLO, I am thinking that maybe they were originally service panels but the service was redone and moving some time ago...
Thanks

 

[Dennis Alwon]

That is not a parallel setup and each 4/0 is improperly protected unless there is a tap rule that applies. I didn't check.

 

[electrofelon]

Right, I agree not really paralleling if not joined both ends. Ways to fix it as I see it:
1. Install 200 OCPD to supply each set.
2. How about this: Join the conductors at the load end to make them parallel conductors and then use tap conductors and the tap rules to supply each 200 amp panel. Only thing is could not use MLO panels, would have to used main breaker to protect the panel at their rating because the feeder is 400 amp and it doesnt matter that it is a "200 amp tap". I believe this to be compliant but wouldnt mind a confirmation (I know I said in the OP that the panels were already main breaker but they are getting replaced and I had originally thought of replacing with MLO to save $$.)

 

[iwire]

2. How about this: Join the conductors at the load end to make them parallel conductors and then use tap conductors and the tap rules to supply each 200 amp panel.

IMO what you describe could be 100% code compliant.

But at the same time 'odd' enough to have issues (unfounded as they would be) with the inspector.

Only thing is could not use MLO panels, would have to used main breaker to protect the panel at their rating

That is required but the tap rules that you would use also require the taps to terminate in a breaker or set of fuses.

IMO you are good to go.

 

[mcelweec@gmail.com]

What length are the 4/0 s?

 

[electrofelon]

Iwire,

I believe if I used the 10 foot tap rule I would not need a main breaker (but in my case MB needed for different reasons, to protect panels at their rating).

MC,

Length of 4/0 is long, precluding considering them taps, which is what I assume you were getting at?

 

[augie47]

You are correct that 408.36 would require a main in the panel in this situation (that changes if you end up with 200 amp OCP at the source).
The 4/0 would only be compliant if it met one of the tap rules (and your calculated load is 180 amps or less)

 

[Dennis Alwon]

You are correct that 408.36 would require a main in the panel in this situation (that changes if you end up with 200 amp OCP at the source).
The 4/0 would only be compliant if it met one of the tap rules (and your calculated load is 180 amps or less)

I agree and that was my point above. The tap rule works otherwise MB at the subs will not help it to be compliant. The 4/0 needs protection at the source.

Can you add 2- 200 amp breakers in the main panel???

 

[curt swartz]

Assuming that your 4/0 AL's have 90C insulation they are only good for 164 amps after derating since you have more than 3 conductors in the raceway. If you install breakers in the supply panel they would need to be 175 amp max. Your calculated load on each panel needs to be 164 amps or less.

If you decided to connect them together on the load end to make them parallel your supply breaker would need to be not larger than 350 amps.

 

[electrofelon]

Been thinking about this a bit and its interesting that this is very similar to installs I do all the time with services - 400 amp meter with two sets of SE conductors, one to each 200 amp panel. Obviously when we are talking feeders the rules are different and its a no go but I could...almost... see myself absent mindedly doing it this way thinking I was doing a 400 amp service

Anyway, This is a main power feeder to a dwelling unit so I can use 310.15(B)(6), however as you say curt, the 6 CCC in same raceway would be a problem. How does derating work when using 310.15(B)(6) values? Can I use the Resi values and apply the 310.15(B)(2)(a) values?

 

[curt swartz]

310.15(B)(6) is only for the main power feeder. If you have 2 feeders neither is the main power feeder and you need to use T310.16.

 

[augie47]

Assuming that your 4/0 AL's have 90C insulation they are only good for 164 amps after derating since you have more than 3 conductors in the raceway. If you install breakers in the supply panel they would need to be 175 amp max. Your calculated load on each panel needs to be 164 amps or less.

If you decided to connect them together on the load end to make them parallel your supply breaker would need to be not larger than 350 amps.

good catch Curt, I missed the "same pipe" part of the post

 

[jap]

Why not put in a 2 section 400 amp panel and be done with it.

 

[iwire]

Why not put in a 2 section 400 amp panel and be done with it.

4 times the cost.

 

[jap]

4 times the cost.

Not from the solutions I've been reading.

 

[jap]

You say the parrallel conductors are all in the same conduit.

if so, how do they seperate to the (2) 200 amp panels?

Do all of the conductors enter the 1st panel, drop off one set, then feed thru to the 2nd Panel?

or is there a junction box in the feeder where they broke off to the 2 panels?

If all the conductors came into the first panel, I would install a 400a MLO Panel and subfeed the 2nd 200a panel.

If there was a j-box installed in the feeder that seperates the (2) then I'd be considering a Tap. JMHO.

 

[iwire]

Not from the solutions I've been reading.

Yes, even still.

Have you priced a double tub 400 120/240 panel?

 

[electrofelon]

Curt,

Are you saying that I if I make the feeders actual parallel feeders by connecting the load ends, that I still cant use (B)(6) for ampacity? doesnt that section have an "s" in parentheses after the word "feeder"? To me the way the code defines the "main power feeder" does not preclude parallel feeders....

Jap,

There is a wire way under the 2 200's. When you say "....I'd be considering a tap", do you mean like I was proposing in the beginning of the thread? If not what do you mean exactly?

I am thinking making the conductors parallel, tapping off the load end to the two main breaker panels is the cheapest way out. I still have the 6 CCC issue, but the disco is fused so I can replace the 400's with 350's and then I should be golden.

 

[jap]

Yes, even still.

Have you priced a double tub 400 120/240 panel?

I guess it all depends on wether we're talking about what it would cost or what needs to be done to make it as it should be.