3 phase y 100 amp subpanel.

[ram11379]

Let me start by saying this is my first post and I am generaly a residential electrician specializing in old home rewires. With that said I have been asked to run a 100 amp subpanel for a new computer room at a local school. All circuits in panel will be 120 volt.

The closest panel to tap off of is 160' away and is a 3 phase y 225 amp max panel. I am thinking that I need to run a 1/O AL 4 wire w/ground SE from panel to panel. SE because above the drop ceiling is packed and no room to run pipe. The breaker obviously needs to be a 3 phase y coming out and the sub panel needs to be 3 phase y main lug.

Now I ask those of you who are commercial electricians am I about to make a mistake and if so what should I be doing here. I am not very familiar with 3 phase or runs this long, as I said I am a residential electrician I am only doing this job as a favor. Any input would be appreciated.

 

[iwire]

A few things

First, if it can be done with 'SE' it will have to be SER.

1 AWG AL or 3 AWG copper would be fine.

I question if it can be done with SE, is the building already done with NM?

I think 3 AWG/4 wire copper MC cable would be more appropriate.

 

[ram11379]

What is the difference between se and ser?
Copper is insanely priced here right now so I think Al is only option. Is #1 AL ok considering it is over 100' away? And no the existing wiring is in pipe and armored cable.

 

[mdshunk]

Yeah, you're not really going to be able to use SER in that building. You'll either have to pull MC, or build some pipe and pull conductors.

Yes, copper is expensive, but who cares? Just pass it along. It costs what it costs.

 

[mdshunk]

SER is "round" SE cable, since it has an extra conductor. Since you're a resi electrician, you'd know it as "subfeed cable".

 

[chris kennedy]

I think 3 AWG/4 wire copper MC cable would be more appropriate.

Might be hard to work without destroying the ceiling grid. I would bid based on FMC and THHN.

 

[infinity]

SER is "round" SE cable, since it has an extra conductor. Since you're a resi electrician, you'd know it as "subfeed cable".

He needs 5 conductors. Does they make SER with 5 conductors?

 

[iwire]

Might be hard to work without destroying the ceiling grid. I would bid based on FMC and THHN.

I do it all the time, up to 225 amp feeders.

That said how would FMC and THHN be any easier?

 

[iwire]

He needs 5 conductors. Does they make SER with 5 conductors?

Sure, bare, white, black, red, blue.

 

[ram11379]

Ok as all the different options are coming in here... what wire size can we agree on considering the 160" run? And am I correct in assuming I need 3 hots 1 neutral and 1 ground?

 

[iwire]

It costs what it costs.

Agreed.

 

[chris kennedy]

I do it all the time, up to 225 amp feeders.

That said how would FMC and THHN be any easier?

Bob I don't use MC larger than 12. Just seems like it would be a bitch to work that heavy MC through a drop ceiling. You must have MAD skills.

 

[iwire]

You must have MAD skills.

Thanks but no, I just have access to more help when I have to do this.

A 3-4 MC can be handled by two guys most times, 4/0-4 that is another storey. That can destory a ceiling if you don't have enough help.

 

[mdshunk]

He needs 5 conductors. Does they make SER with 5 conductors?

Why? He can just as easily do a single phase panel. In fact, I thought that's what he had in mind.

 

[mdshunk]

Bob I don't use MC larger than 12. Just seems like it would be a bitch to work that heavy MC through a drop ceiling. You must have MAD skills.

No, no. I happen to keep several of those big azz Greenlee pullies on my truck for just this purpose. Keeps the cable off the grid. For the smaller sizes, the "Top Slide" is the cat's back side.

 

[infinity]

Why? He can just as easily do a single phase panel. In fact, I thought that's what he had in mind.

I didn't assume that. For my buck I would install a 3 phase feeder and panel. For 1 extra conductor you'll get a 50% increase in 120 volt circuit capacity.

 

[iwire]

He can just as easily do a single phase panel. In fact, I thought that's what he had in mind.

AHHHH!

I hate a single phase panel supplied from a three phase source.

It never even crossed my mind that he might be running single phase.

 

[mdshunk]

I hate a single phase panel supplied from a three phase source..

Yes, you do seem to have a lot of pent up hatred. If you ever want to talk about it, my door is always open. :smile:

 

[ram11379]

I honestly wasn't sure if I was going to run a 3 phase or single phase panel. I guess that is why I am here . If I go 3 wire w/g(single phase) I am limiting this panel to only 120 volt usage correct? Also still waiting on the opinions of WIRE SIZE. By the way thanks everyone for all the help.

 

[mdshunk]

If I go 3 wire w/g(single phase) I am limiting this panel to only 120 volt usage correct?

Nope. You'll be able to do 120 and 208 loads. Just won't be able to power any 3-phase loads.

Hard to say about the gauge for sure, because you havn't provided any load data. At 160 feet, depending on the load, it would be between #2 and #3 more than likely.