Shop Power Question

[Augus7us]

Hey Guys,

I'm trying to research how to wire up power to the shop. My goal is to replace the existing power, a 30AMP breaker, with 100AMP service. My main issues are wire type and how to run it.

From reading up I'd prefer to go with copper over aluminum. From what I've read 4AWG will work but may only give me 90AMPs. I'm also on the fence about what type of wire; THWN in conduit or some type of service entrance cable rated for under ground burial. The run will be around 90ft from my breaker box to the sub panel in the shop. When trying to read up on this I find a lot of contradictory information. I'm hoping you guys can help me out without me having to buy and interpret the code book.

To sum it up here are the questions I'm trying to answer:

Should I run this in conduit or not? Is one more advantagous than the other?

Depending on my choice in question #1 what type of wire should I purchase?

How do I transition it in the house? I.e. if I run it in conduit underground does it have to be in conduit in the house?

I'm sure I'll have many more questions as I progress but I figured this is a good place to start.

Thanks

-Clint

 

[blair683]

Why do you want copper over aluminum? Copper is significantly more money. I ran 100 amp to my shop from my house. The total run was around 85'. I used the aluminum Mobile Home Feeder (MHF). MHF consists of three #2 Aluminum wires and a #4 aluminum wire. It is direct burial but I buried it in conduit. It is only $1.45 a foot at home depot (copper feeder wire would be about 5x this amount). I found it cheaper at my local electrical supply store. Below is a picture of how it enters my garage. The house would depend on where your breaker panel is located (basement, first floor, opposite side of the house from the garage).

 

[Augus7us]

Thanks Blair, I should have clarified how this would be ran once inside the house. I'll try to fire up photoshop and make a diagram.

It will come into my house in the basement. About 40' of the run will be in the house traversing the basement ceiling to the breaker box. I'll have to go through my floor joists as they are perpendicular to the run.

To be honest, I was going with copper because it seemed to be the most recommended choice from all the stuff I read and it doesn't have the shrinking and swelling issues aluminum seems to have. Again just going off what I read.

-Clint

 

[blair683]

I don’t know much about drilling through floor joists but I am guessing it’s a big no no as you would be compromising the structural strength of the joists. I would rather go under the joists before I would go through them. Can you bury it outside to the side of the house that has the panel then enter the basement there? Then straight up to the panel.

 

[Augus7us]

Unfortunately no, I'd have to go under my deck or my driveway. There are holes in the joists now for plumbing and some electrical but I don't think they are as big as I would need for 3 or 4 AWG wire. I don't have any to see. But its a good point, can I run wire of this diameter through the floor joists or would I have to run it under them? Fortunately that side of my basement is not finished so I could getaway with it if I had to.

-Clint

 

[wyliesdiesels]

Hey Guys,

I'm trying to research how to wire up power to the shop. My goal is to replace the existing power, a 30AMP breaker, with 100AMP service. My main issues are wire type and how to run it.

From reading up I'd prefer to go with copper over aluminum. From what I've read 4AWG will work but may only give me 90AMPs. I'm also on the fence about what type of wire; THWN in conduit or some type of service entrance cable rated for under ground burial. The run will be around 90ft from my breaker box to the sub panel in the shop. When trying to read up on this I find a lot of contradictory information. I'm hoping you guys can help me out without me having to buy and interpret the code book.

To sum it up here are the questions I'm trying to answer:

Should I run this in conduit or not? Is one more advantagous than the other?

Depending on my choice in question #1 what type of wire should I purchase?

How do I transition it in the house? I.e. if I run it in conduit underground does it have to be in conduit in the house?

I'm sure I'll have many more questions as I progress but I figured this is a good place to start.

Thanks

-Clint

What will your loads be?

Thats the key thing to know before sizing the feeder.

Best bet will probably be #2 al MHF which will limit you to 90a.

You will need an isolated neutral bar in the sub plus a grnd bar kit and 2 grnd rods.

Best to put it in conduit underground as cheap insurance against failure due to rocks etc.

If conduit indoors is an issue, you can transition to SER indoors which can be ran in the same method as NM-b aka Romex.

Why do you want copper over aluminum? Copper is significantly more money. I ran 100 amp to my shop from my house. The total run was around 85'. I used the aluminum Mobile Home Feeder (MHF). MHF consists of three #2 Aluminum wires and a #4 aluminum wire. It is direct burial but I buried it in conduit. It is only $1.45 a foot at home depot (copper feeder wire would be about 5x this amount). I found it cheaper at my local electrical supply store. Below is a picture of how it enters my garage. The house would depend on where your breaker panel is located (basement, first floor, opposite side of the house from the garage).

#2 al used in that application is limited 90a...

 

[blair683]

In my area I did not need a separate ground rod at the sub panel (at the garage). The copper ground at the house was good enough. The sub panel does have a seperate ground and neutral bar. My run was 85 feet and the local electrical supplier claimed it would be fine at 100amp. I smacked a 100amp breaker on it because the 90a was a lot more money (less common). I never plan to test it at 90 or 100 amp anyway. Although I am sure Wylie is correct with 90amp because of the long run. Spend the extra $20 and put a 90amp breaker on it to be safe. If I were you I would run it in conduit under your floor joist just use a clamp/ hanger and hang the conduit to the bottom of the joists. I feel like if you decide to go through the joists you should get a structual engineer to ok it.

 

[wyliesdiesels]

In my area I did not need a separate ground rod at the sub panel (at the garage). The copper ground at the house was good enough. The sub panel does have a seperate ground and neutral bar. My run was 85 feet and the local electrical supplier claimed it would be fine at 100amp. I smacked a 100amp breaker on it because the 90a was a lot more money (less common). I never plan to test it at 90 or 100 amp anyway. Although I am sure Wylie is correct with 90amp because of the long run. Spend the extra $20 and put a 90amp breaker on it to be safe. If I were you I would run it in conduit under your floor joist just use a clamp/ hanger and hang the conduit to the bottom of the joists. I feel like if you decide to go through the joists you should get a structual engineer to ok it.

Whoever told you that about not needing electrodes on detached structures is wong. It is required by the NEC and is for lightning suppression.

If your system is relying on a rod on another building, you will be more suspectable to lightning damage. Plus its more likely to induce lightning current into the house circuits vs having the electrodes at the detached building.

The 90a requirement has nothing to do with distance. it has to do with the ampacity rating of the wire.

See Table 310.15(B)(16)....

 

[blair683]

A bunch of people on here told me that the ground rod on my house was fine. The local electric supply house said the same. That's how I did it. Maybe one day in the future, I'll smack a copper rod in the ground out there and run it to the sub panel. It has been the way it is for a year now. I understand that the MHF is rated for 100 amp if it is supplying the entire load to a building but only 90 amp on a sub panel.

 

[sberry]

It's worded different, it's the entire load of the service. I use 60 most of the time and I used 70 on a couple cause I got a deal on them. I never fixed one, never got a call due to a trip.

 

[blair683]

Yins are making me spend money! Lol! I will probably end up putting a little smaller breaker in my main panel for the feed to the garage. I never plan on using anywhere near the 100 amp at once anyway. I will also end up putting a copper ground rod at the garage. Sorry for kind of getting this thread off track.

 

[Augus7us]

What will your loads be?

Thats the key thing to know before sizing the feeder.

Best bet will probably be #2 al MHF which will limit you to 90a.

You will need an isolated neutral bar in the sub plus a grnd bar kit and 2 grnd rods.

Best to put it in conduit underground as cheap insurance against failure due to rocks etc.

If conduit indoors is an issue, you can transition to SER indoors which can be ran in the same method as NM-b aka Romex.

My load currently at most would be lights, stereo etc plus my kiln and a welder. The kiln is 30a 220 and the welder is 50a 220. I'd like to get the full 100 just to be safe and because I'd rather have too much than not enough, in fact I tried getting 200AMP in the house and in the shop but it was too much effort and money.

Is there one option where I can run the same wire from the shop to the house panel? I'm not opposed to some kind of disconnect and switching wire types at the house but I'd prefer running one cable.

-Clint

 

[pattenp]

A bunch of people on here told me that the ground rod on my house was fine. The local electric supply house said the same. That's how I did it. Maybe one day in the future, I'll smack a copper rod in the ground out there and run it to the sub panel. It has been the way it is for a year now. I understand that the MHF is rated for 100 amp if it is supplying the entire load to a building but only 90 amp on a sub panel.

So...who is this bunch of people that you speak of?

 

[Norcal]

A bunch of people on here told me that the ground rod on my house was fine. The local electric supply house said the same. That's how I did it. Maybe one day in the future, I'll smack a copper rod in the ground out there and run it to the sub panel. It has been the way it is for a year now. I understand that the MHF is rated for 100 amp if it is supplying the entire load to a building but only 90 amp on a sub panel.

That only applied to the entire load of a dwelling only, not a "building", the table allowing #2 AL to be used for a 100A dwelling service has been removed from the NEC, now calculations are required to be able to undersize the conductors.

2 ground rods are required 6' apart or more, unless you can prove 25 ohms of resistance or less, the testing equipment is expensive & need to be qualified to use it, simpler & cheaper to just drive the 2nd rod.

 

[alfredeneuman]

the table allowing #2 AL to be used for a 100A dwelling service has been removed from the NEC, now calculations are required to be able to undersize the conductors.

Although the table has been removed, the calculations required end up with the same numbers as in the old table.
As Norcal said, it doesn't apply in this case.

 

[wyliesdiesels]

A bunch of people on here told me that the ground rod on my house was fine. The local electric supply house said the same. That's how I did it. Maybe one day in the future, I'll smack a copper rod in the ground out there and run it to the sub panel. It has been the way it is for a year now. I understand that the MHF is rated for 100 amp if it is supplying the entire load to a building but only 90 amp on a sub panel.

Who told you this and which threads was this on?

Whoever said it, is wrong.

And you missed a key word in that last sentence- DWELLING!!

 

[Bretny]

I have 100ft from main pannel. 100a service to my garage. Did #2 DB wire. Believe its aluminum and have had no issues. Run another piece of pipe, conduit or black water pipe in the hole. You will want some other wire out there in the future its a guaranteed.

Also if your not paying someone to do this make sure you measure the piece of wire you get before you fill the trench back in.

 

[blair683]

[/b]

Who told you this and which threads was this on?

Whoever said it, is wrong.

And you missed a key word in that last sentence- DWELLING!!

I remember reading it on a thread before, if it’s super important I can try searching for it. Either way I’ll add a copper rod at my subpanel. Now that I know better.

 

[mike93lx]

I remember reading it on a thread before, if it’s super important I can try searching for it. Either way I’ll add a copper rod at my subpanel. Now that I know better.

You need two rods...read the posts