Tapping off a wireway

[mshields]

I've got a 350kW generator with a 600A main feeding into a wireway off of which I want to tap for my Life Safety, Critical branch, Equipment branch, etc (obviously for a hospital).

My concern is that I'll have two conductors per phase comming into that wireway and will have to tap off via each phase to each branches breaker.

I normally stear clear of tapping off a wireway like this when I've got multiple conductors per phase but with the 2008 codes isolation requirements for emergency distribution systems, I prefer to go this route to having a huge switchboard with each section having a single, relatively small circuit breaker.

I'm wondering what kind of trouble I might get into here when the electrician goes to actually implement this. The first thing that occurs to me is that the minimum size for parallel conductos is a 1/0. So for my feed to my 150A LS ATS, I'll need to come off with two 1/0's.

Do you agree?

Any comments would be appreciated.

Thanks,

Mike

 

[chris kennedy]

The first thing that occurs to me is that the minimum size for parallel conductos is a 1/0. So for my feed to my 150A LS ATS, I'll need to come off with two 1/0's.

Do you agree?

No sir, one 1/0 will do.

From 08 NECHB

Where individual conductors are tapped from conductors in parallel, the tap connection must include all the conductors in parallel for that particular phase. Tapping into only one of the parallel conductor would result in unbalanced distribution of tap load current between parallel conductors, resulting in one of the conductors carrying more than its share of the load, which could cause overheating and conductor insulation failure. For example, if a 250-kcmil conductor is tapped from a set of two 500-kcmil conductors in parallel, the splicing device must include both 500-kcmil conductors and the single 250-kcmil tap conductor.

 

[chris kennedy]

Mike, what size is the wireway? If the two 350's can be pulled from the main back to the wireway, I would use IPLD 500-5. I would pass the 350's through two ports of the polaris and tap away. Makes for a nice neat install.

 

[mshields]

Great input!

Great input!

Thanks Chris

This is a new installation so I can make the wireway any size I want.

Guess I never read the last part of that paragragh from the code indicating that while you do need to tap both conductors that does not preclude two conductors feeding into one.

As for the Polaris cat number - that's great too.

Thanks again,

Mike

 

[Fast__Eddie]

Maybe totally misunderstood the question but, can you add additional o/c protection @ genset to avoid taps??

 

[Mike01]

taps

taps

what about power distribution blocks like thoes manufactured by ilsco or cooper bussmann these seem to work well with multiple (parallelled) line condutctors and indivigual secondary load conductors for multiple panels.

 

[benaround]

what about power distribution blocks like thoes manufactured by ilsco or cooper bussmann these seem to work well with multiple (parallelled) line condutctors and indivigual secondary load conductors for multiple panels.

This is the way I like to do it also.

 

[mshields]

Breakers at the generator

Breakers at the generator

One could do it that way. In this particular instance, the generator is outside and I'm trying to avoid all those feeders comming into the building. Also, given that it is a hospital and given that in Mass, we need two critical branches, and given that the breakers need to be oversized to meet NEC Art 700 coordination requirements, we'd need a custom generator enclosure to accomodate all of this.



Mike

 

[elec_eng]

From 08 NECHB

Where individual conductors are tapped from conductors in parallel, the tap connection must include all the conductors in parallel for that particular phase. Tapping into only one of the parallel conductor would result in unbalanced distribution of tap load current between parallel conductors, resulting in one of the conductors carrying more than its share of the load, which could cause overheating and conductor insulation failure. For example, if a 250-kcmil conductor is tapped from a set of two 500-kcmil conductors in parallel, the splicing device must include both 500-kcmil conductors and the single 250-kcmil tap conductor.

I am still on 2005. Which section is this?

 

[elec_eng]

I am still on 2005. Which section is this?

I guess I found it. 310.4.