Wire sizing help

[CoryF]

Hi all,

First off thanks for all the great info in this forum, has really made my plan to power a building about 210' (panel to panel) away seem feasible. My research from this forum and else where has lead me to think at that distance, with voltage drop, the "garage journal standard" 2-2-2-4 MHF would be good for 60 amps. I think that would be plenty for me (17x30 "outbuilding" for a 1 man woodshop). My problem is it doesn't seem Siemens 60 amp breaker takes 2-wire and I'd rather not deal with junctions or splices if I can avoid it. Also whole run will be in 2" conduit (already purchased and had a deal I couldn't pass up) So my question then becomes:

A) Is there a Siemens 60 amp breaker that will take 2-gauge wire?

or

B) Can I upsize to 1-gauge USE-2/RHH/RHW-2 wire and use a 70amp breaker, which will take up to a 2/0. If so, what size should I use for the neutral and ground?

Thanks!

 

[justsam]

Why not just use a 90 Amp breaker? The breaker is there to protect the wire and the wire is indeed rated for 90 Amp.

 

[CoryF]

Based on voltage drop at 210' ft, 90amp would be too much for 2 gauge wire is my understanding.

 

[sberry]

I am not sure about Siemens. sqd takes a 2 with 60. I also usually limit the breaker on long runs, I have 3 or 4 of them exactly the same, 200 plus ft and fed 50 or 60.

 

[Bert_]

Up-sizing wire for voltage drop is not a code rule. There is a fine print note it the code that recommends keeping voltage drop for feeders under 3%, but it is exactly that a recommendation, it is NOT required.

It is best to consider voltage drop with long wire runs but you need not to think of it as a hard rule.

Voltage drop is all about how much load is on the wire, Not just the size of breaker. Your wire is large enough for a 90A breaker, so you can use one.

Unless your trying to start large motors or something with a huge startup draw, using that wire at 210' voltage drop will not be a problem even with a full 90A of load

 

[sberry]

I agree the numbers are not critical but distance does effect it in regards to short circuit interruption. I an not sure the difference between 60 and 90 breakers, where this threshold would be? A 60 cost a lot less than a 90.

 

[wyliesdiesels]

Why not just use a 90 Amp breaker? The breaker is there to protect the wire and the wire is indeed rated for 90 Amp.

Because of voltage drop.

Based on voltage drop at 210' ft, 90amp would be too much for 2 gauge wire is my understanding.

If u do #2 AL MHF on a 70a breaker, voltage drop would be 3.1% @ max load so u should be fine.

EDIT: it appears that i was mixing up my cir mils when i did the calcs the other day. Whoops

#2 al on a 70a breaker over 210' would be 3.9%. 60a would be 3.4% and 50a would be 2.9%...

 

[justsam]

I agree that the feed voltage drop is greater than the RECOMMENDED 3%. It is something like 3.7%. The RECOMMENDED branch/feeder combination is less than 5%, so in a one man, 17x30 shop I made the assumption that the combination would be less than 5%.

 

[CoryF]

Thanks all, I'll go ahead and use a 70amp. I just didn't want to give inpsector anything to flag. Now to rent a trencher and start digging.

 

[gnab2]

210' at 60A with 2/0 AL will put you at 3.1 volts of drop or 2.58% for a end result of 116.9 VAC single phase. I would go larger if possible, for that just in case you want more later.

With lights all on, large fan running, compressor running and a welder running you will be at 50-60 amps. That is with out a beer fridge or anything else. Just saying...

I know that it is an upfront cost but it is a not a headache you want to have later.

 

[CoryF]

Not likely a welder in this shop. Mostly wood tools, and mostly 240v (TS, planer, jointer, DC, etc) If I did want to go to next MHF size, will 2/0-2/0-1-4 MHF fit in 2" conduit or be too hard to pull? 160ft longest run between pull points (LB at shop and house), another 40ft in basement.

 

[ard]

Thanks all, I'll go ahead and use a 70amp. I just didn't want to give inpsector anything to flag. Now to rent a trencher and start digging.

FWIW- rent the largest piece of equipment you can either (a) fit on the property or (b) pull with your truck.

AWD articulated trencher with a 6"x48 deep boom is my goto. Even for little 24" deep runs. I'd rather spend 2x the money and do it in 1/3 the time!

Toss a water line and two other conduits in the trench. Just in case.

 

[wyliesdiesels]

210' at 60A with 2/0 AL will put you at 3.1 volts of drop or 2.58% for a end result of 116.9 VAC single phase. I would go larger if possible, for that just in case you want more later.

With lights all on, large fan running, compressor running and a welder running you will be at 50-60 amps. That is with out a beer fridge or anything else. Just saying...

I know that it is an upfront cost but it is a not a headache you want to have later.

your math is a bit off.

2/0 AL would give 4volt drop and 3.1/240 is 1.29% NOT 2.58%....better check the batteries in the calculator...

2/0 is way overkill in this situation...

#2 al would be 8v drop @ 60a load which is 3.4%...

 

[sberry]

I have wired 2 dozen garages with 2 alum and a 60A breaker,,, never,,,, never had one call about a trip and a couple of them had real work going on for decades. One of them I welded a fair amount from, he had a 5 hp comp on it too, but I simply didn't strike an arc if the air was running.
I ran a welding shop from one a winter, air was on another circuit but 3 500 watt lights, 2 wire feeders, a 200 and a 250, 220 ft long circuit.

 

[mrobins297aaa]

the panel in my barn is 170' front the main in the house, I fused it at 100 amps and used 2/0 al wire...........the inspector said he was ok with it and approved it.

I might be wrong but when I installed the 100 amp breaker in the main panel I remember think that's was about the maximum size wire that breaker would take.

 

[wyliesdiesels]

the panel in my barn is 170' front the main in the house, I fused it at 100 amps and used 2/0 al wire...........the inspector said he was ok with it and approved it.

I might be wrong but when I installed the 100 amp breaker in the main panel I remember think that's was about the maximum size wire that breaker would take.

2/0 is overkill for that as well.

@ max load that is only 5.4v drop or 2.3%...

1/0 wouldve been fine. 6.8v or 2.8%...

 

[mrobins297aaa]

2/0 is overkill for that as well.

@ max load that is only 5.4v drop or 2.3%...

1/0 wouldve been fine. 6.8v or 2.8%...

Thanks, better than underkill I guest. probably that's why the inspector didn't have a problem with it.

I have to add a ground rod to that panel in my barn, any idea what size wire should I run?

 

[wyliesdiesels]

Thanks, better than underkill I guest. probably that's why the inspector didn't have a problem with it.

I have to add a ground rod to that panel in my barn, any idea what size wire should I run?

Did u run 4wires to the panel?

minimum size is #8 cu but would need to be in conduit.

Max size is #6 which can be bare solid and doesnt have to be in conduit as long as its not subject to damage(eg string line trimmer...)

 

[klassenl]

Up-sizing wire for voltage drop is not a code rule. There is a fine print note it the code that recommends keeping voltage drop for feeders under 3%, but it is exactly that a recommendation, it is NOT required.

It is best to consider voltage drop with long wire runs but you need not to think of it as a hard rule.

In Canada it is a RULE. A hard and fast RULE. How it is enforced is a different conversation.

 

[mrobins297aaa]

Did u run 4wires to the panel?

minimum size is #8 cu but would need to be in conduit.

Max size is #6 which can be bare solid and doesnt have to be in conduit as long as its not subject to damage(eg string line trimmer...)

yes I have 4 wires the neutral and ground are separate in the sub panel.
I ran 2/0,2/0,2/0,1

 

[mrobins297aaa]

thanks for the info

 

[Bert_]

In Canada it is a RULE. A hard and fast RULE. How it is enforced is a different conversation.

Good to know, as I am not familiar with Canada's electrical code. Stuff like this can also be required in some cities that create additional rules above and beyond the NEC.

It is always good practice to consult your local authority. Not that it's bad to get advise on a forum but keep in mind some of the advise given may not pertain to your area, especially if you live in a different country than the majority of the posters or if you have many local rules in addition to NEC/ect.

 

[CoryF]

Because of voltage drop.



If u do #2 AL MHF on a 70a breaker, voltage drop would be 3.1% @ max load so u should be fine.

EDIT: it appears that i was mixing up my cir mils when i did the calcs the other day. Whoops

#2 al on a 70a breaker over 210' would be 3.9%. 60a would be 3.4% and 50a would be 2.9%...

Hi Wylie, just saw your edit. Based on that I'm back to my problem I think? I'm thinking I should bump to 1 and use a 70amp feed. Based on calculator here http://www.nooutage.com/vdrop.htm 70amp would be 3.1% drop. If I went 1gauge individual connectors, what would minimum neutral and ground wire be?

Thanks
Cory

EDIT: Disregard.. heard back from inspector and he was fine with 2-2-2-4 and 70 amps. That's good enough for me.

Thanks

 

[wyliesdiesels]

If you are a one man shop and have only a few large loads on you should be fine....Doubt u will max it out....