120/208 volt, 1200 amp-paralled feeders

[ohms277]

Can 3- 4" conduits with 4 -500mcm cu. conductors be paralled. It's a long story!

 

[raider1]

Can 3- 4" conduits with 4 -500mcm cu. conductors be paralled. It's a long story!

They can be paralleled but you can not protect the feeder with a 1200 amp overcurrent protective device.

3 paralleled 500 Kcmil copper conductors have an ampacity of 1140 amps and 240.4(B) does not permit you to use the next size up overcurrent protective device for feeders over 800 amps.

Chris

 

[raider1]

By the way welcome to the forum.

Chris

 

[augie47]

They can be, but you non-adjusted ampacity would be 1140 amps so Code compliance would depend on the calculated load and on what they feed (motor, MLO panel, MB panel, etc)

(sorry Chris, stepped on you,.,,my computer is ill and uploads take a while)

 

[petersonra]

I don't see why not as long as the conductors are equal length, and you can deal with the ampacity problem others have mentioned.

 

[ohms277]

I have inherited this project, and the previous electrician built a 1200 amp service to feed the existing building with 800 amps and the new add-on with 400 amps. So what we have at the transformer pole/rack/service is 2-4" risers with 4- 1000 mcm in each 4", a gutter, below it is a 800 amp disconnect for the existing building and a 400 amp. disconnect for the future add-on. Problem is the two 4" risers have no weather-heads as the previous electrician broke four heads trying to get them on, and they haven't been seen since. So before I put hands on this, I had the paralleling question. But now it seems that the power utility wants 2-6" risers, since none of their drawings or specs has ever showed more than two conduits. Told you it was a long story. Do they even make a 6" weather-head?

 

[Cow]

I couldn't tell you about the 6" weatherhead but damn it'll be big......

It's my understanding that since you're feeding more than one service disconnect, your service conductors are sized to the load rather than the combined OCPD of your service disconnects. 230.42(A)

 

[augie47]

I agree with Cow on both counts.

 

[Robert Hutcherson]

• First determine the calculated load on the service.
• If the service calc is less than 1000amp, add a 3rd 4" conduit riser and install 3 sets of 400mcm copper.
• If the service calc is above 1000amp and below 1200amp, add a 3rd conduit riser and install 3 sets of 600mcm copper.
• Does the service conduits terminate into a CT Cabinet and then go to service gutter to feed the 800amp and 400amp service mains?
• You could consider eliminating the service gutter and go from the loadside of the CT Cabinet directly to the 800amp and 400amp service mains.
• Just some ideas that may help resolving the issues.
• Good luck.

 

[Smart $]

I couldn't tell you about the 6" weatherhead but damn it'll be big......

It's my understanding that since you're feeding more than one service disconnect, your service conductors are sized to the load rather than the combined OCPD of your service disconnects. 230.42(A)

I agree with Cow on both counts.

I always have had a problem with the way 230.42(A) especially (A)(1) is worded. It states "The sum of the noncontinuous loads plus 125 percent of continuous loads." It DOES NOT state something to the effect of "shall have an ampacity not less than the calculated load to be carried, determined in accordance with Part III, IV, or V of Article 220, as applicable", similar to the wording in 230.79. As it is currently worded, to me that's saying one cannot apply any demand factor to the load when sizing the service entrance conductors...

On the point that Chris brought up, about the OCPD rating, for service conductors, that requirement is 230.90(A)... "Such protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor."

 

[augie47]

Samrt$, Very interesting comments..cause for thought.
Note, hoever, in regard to 230.90, there are exceptions to the basic statement you quoted which allow for calculated load.

 

[ohms277]

All metering to be done on pole by power company. Thanks for your input.

 

[Smart $]

Samrt$, Very interesting comments..cause for thought.

Indeed it is. A 2014 proposal in the making...

Note, however, in regard to 230.90, there are exceptions to the basic statement you quoted which allow for calculated load.

Oh, I know. I was just pointing out the general section comparable to 240.4(B) that Chris commented on, but only applies to feeders, and had since been clarified that we are discussing service conductors... but I suppose I should have elaborated...