100amp Sub Panel 75' Correct Wire? (yes again)

[cturboaddict]

So, I'm getting setup for my garage wiring. I've bought all the necessary "inside" wiring components for the detached garage, and had an electrician come by. I wanted to get a quote to have them wire it for me, and add a whole home surge protector while they were there. I told them I would do the digging, and to just have them run the feeder wire and hookup the main panel and sub panel. Along with hooking up my home runs inside the garage to the sub panel. The quote came back at $1800 which felt a little high if I calculated the material myself to be around $250 max for a 2-2-2-4 SER aluminum cable. Some of the guys statements about no ground needed, seemed a bit off to me. So I checked codes, and my local inspector confirmed my suspicions. He also said that he has inspected alot of this electricians work, but I am more than welcome to the wiring myself if I wanted to.

Here's the details.
200amp Service in Home- 6 open spaces currently.
100amp sub panel in garage. Bought same brand as main panel.
Garage is 26'x28'x11' ceilings.
13' from house detached, total of 75' max wire length run to sub.
Outside the home will be underground in 2" sch 40 PVC with 2 LBs and sweeps 18" below ground.
Incorporated UFER into foundation when pouring, it's approx 28' (50' wire distance from sub panel)
County uses 2008 NEC code.

Can I use a 2-2-2-4 SER Aluminum cable to carry the 100amp breaker at the main to the 100amp breaker at the sub? I keep finding that it's only rated at 90amps.

What size wire do I need to use for a true 100amp? If it's larger than a 2-2-2-4 alum, will the 100amp breaker accept a larger wire size?

Would I know the difference if I only had a 90amp feed? I plan to have a 220v HVAC mini split system, 220v for a multimatic welder, 220v compressor. And a host of standard 20amp outlets approx 10 total between inside and out and 15amp lighting. Outlets will have GFIs.

What is the difference between SER and MHF (both are available in the same size locally). If a mobile home feeder is used, I'll need to run it in PVC inside the home as well, correct?

I'm just wanting to make sure that I have the correct wire, and what my wire options are. Or if I'm overthinking this thing totally.

Thanks in advance guys!

 

[pattenp]

SER can not be used under ground, even in conduit. You need THHN/THWN, MHF, or XHHW wire.

Also #2 Al is only rated for 90A. You need #1 Al for 100A.

100A breaker should take up to 2/0.

MHF has to be in conduit where exposed above ground and inside the structure.



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[cturboaddict]

SER can not be used under ground, even in conduit. You need THHN/THWN, MHF, or XHHW wire.

Also #2 Al is only rated for 90A. You need #1 Al for 100A.

100A breaker should take up to 2/0.



*

Weird, that's what the electrician's quote said he was going to use. SER.
I just talked with him and he said it was 2-2-2-4 Copper Service cable. Inside a conduit.

 

[D45]

I have a Square D QO 100amp sub panel, that is fed from the house's main 200amp panel

I have 6 circuits in the subpanel and it is fed by #4, I believe

 

[cturboaddict]

How far is the run?

 

[wyliesdiesels]

Weird, that's what the electrician's quote said he was going to use. SER.
I just talked with him and he said it was 2-2-2-4 Copper Service cable. Inside a conduit.

Is he specifically calling it SER?

If so, then he's using the wrong cable. Cant use SER underground regardless of conduit.

And #2 CU is oversized for 100a.

 

[wyliesdiesels]

I have a Square D QO 100amp sub panel, that is fed from the house's main 200amp panel

I have 6 circuits in the subpanel and it is fed by #4, I believe

Is that attached or detached?

 

[Falcon67]

IMHO, you can save a lot of $ using MHF. I have a 24x40 with a LOT of power stuff, dual AC units, heat, about to put in a 30A RV connection, big power tools, welder, well pump, etc, etc. It's fused at 70A on MHF and no trips.

 

[ard]

OP you prolly need 40a Max for what you are planning, load wise. I wouldn't sweat 90 vs 100.

 

[cturboaddict]

Is he specifically calling it SER?

If so, then he's using the wrong cable. Cant use SER underground regardless of conduit.

And #2 CU is oversized for 100a.

Yes, specifically called out SER.
Stuff is expensive. But they will warrant it that way.

Also said that I didn't need a seperate ground. I called BS on him and threw the code to him, and double checked with the inspector. I've already setup a UFER in the foundation to tie into. He told me his is going to double check it and call me back.

 

[cturboaddict]

IMHO, you can save a lot of $ using MHF. I have a 24x40 with a LOT of power stuff, dual AC units, heat, about to put in a 30A RV connection, big power tools, welder, well pump, etc, etc. It's fused at 70A on MHF and no trips.

Electrician told me we cannot run Aluminum in the house. Said the county won't allow it anymore.

 

[cturboaddict]

OP you prolly need 40a Max for what you are planning, load wise. I wouldn't sweat 90 vs 100.

 

[Falcon67]

Electrician told me we cannot run Aluminum in the house. Said the county won't allow it anymore.

Interesting - but the locals make the call. Here, no problem.

 

[antinym]

Also #2 Al is only rated for 90A. You need #1 Al for 100A.
*

I'm no electrician, But the NEC chart says 90 degree rated AL is good for 100A.

Am I reading that wrong?

 

[alfredeneuman]

I'm no electrician, But the NEC chart says 90 degree rated AL is good for 100A.

Am I reading that wrong?

The 90 degree column is used mostly for derating purposes.
The lugs on the breakers are only rated for 75 degrees (some older breakers are rated at 60), and determine the overall ampacity of the conductor.

 

[Norcal]

I'm no electrician, But the NEC chart says 90 degree rated AL is good for 100A.

Am I reading that wrong?

Yes you are. The ninty degree column is only used when derating conductors never when sizing conductors.

 

[wyliesdiesels]

Yes, specifically called out SER.
Stuff is expensive. But they will warrant it that way.

Also said that I didn't need a seperate ground. I called BS on him and threw the code to him, and double checked with the inspector. I've already setup a UFER in the foundation to tie into. He told me his is going to double check it and call me back.

Time to get a different electrician if he thinks SER is permitted for use underground and thinks no grounding electrode is required for a detached.

This guy doesnt know what he's doing...

 

[sberry]

I tend to agree, 2 or 3 or more things wrong on one of the most common and simple installs there is, got to make one wonder where they learn this.

 

[cturboaddict]

Just made me uneasy.

 

[sberry]

I can see why. There is absolutely no reason a qualified hand should need to ask an inspector anything about this common installation. Doesn't mean it wont get done in the end or that it wont work but certainly makes a guy wonder when some of it is so fundamental and hasn't changed for a good long time.
I think the inspector was hinting that it might be a good idea to do it yourself.
We had a local journeyman that worked for a few outfits, thankfully he doesn't any more but I must have followed him around a dozen jobs and never seen one pass on the first try. He did one out in the sticks, actually called for an inspection of a single circuit to a garage and was shot down, not even science but buried the wire only 6 inches. Seems if I was going to call for insp would at least bury the wire deep enough especially considering it was only about 10 ft long. Had to replace it as it wouldnt reach.
The advice you get from a forum like this is usually very good, its looked over by several masters. There are plenty of guys that do it right and you could ask and get it straight but I always got to wonder when the blanket answer is to ask a local electrician instead of answering the question, Joe Hometime usually doesn't know enough people to know who does what.
Maintenance electricians are often really bad about this as are handyman types.

 

[cturboaddict]

I deal in contracts daily. And last thing I need is a bunch of change orders because someone is incompetent. I think I'm going to get a second quote from someone else, or just end up running this myself. (I'm stubborn, so running it myself is highly likely)

 

[D45]

Is that attached or detached?

Attached garage addition

 

[rburke65]

I'd look for another electrician. Aluminium ROMEX can't be used in a house is maybe what he's talking about. I have installed lots of alum. cable. I have it feeding my pole barn and my shop.

 

[Norcal]

I'd look for another electrician. Aluminium ROMEX can't be used in a house is maybe what he's talking about. I have installed lots of alum. cable. I have it feeding my pole barn and my shop.

AL NM "Romex" cable is still code compliant, just not going find any being sold. . Any NOS, New Old Stock AL NM cable can't be used because it does not have the required ninty degree rating.

 

[wyliesdiesels]

I'd look for another electrician. Aluminium ROMEX can't be used in a house is maybe what he's talking about. I have installed lots of alum. cable. I have it feeding my pole barn and my shop.

Southwire no longer makes al romex

And if you meant any type of al wiring in a house isnt allowed thats incorrect.

 

[Falcon67]

That did sound odd, should be able to pull MHF in a 2" conduit to get it done. In fact here, the inspector even said he'd approve conduit or not. So I not.