[NatePit09]

I have got all of the wiring done in my garage to turn it into a functioning workshop with 5 separate circuits complete with a 100 Amp breaker box. I have purchased sched 40 PVC conduit to run my lines from my house out to the garage, and all of the pieces to complete the run. My question is this: what size wire do I need to run from the main panel in the house to the new sub - panel in the garage and what size breakers do I need to purchase? The new wiring in the garage is all 14-2 and consists of a maximum of 5 device boxes on each circuit. The distance from the main panel in the house to the new sub - panel is approx. 70'. Do I need to install a grounding rod for the new sub - panel, and if I do, how do I do that? The new sub - panel is rated for 100A. There isn't going to be anything running in the shop stronger than basic power tools, with the exception of a table saw or a band saw.

[stanfortyman]

This is one of the most asked about topics: Ask Me Help Desk - Search Results

[KISS]

It. Is. Will have to come back to wire size.

14-2 necessitates 15 A breakers.

Ground rod - required if structure is detached

Sub-panel - 4 wire connection.

Sub panel - neutral to ground bonding screw must be removed

Sub panel - usually ground bar kit needs to be purchased

Wire - THWN can be use din conduit. Considered wet loacation. Buried 18" deep. Direct burial cable can also be used.

Wire - Aluminum or copper

Conduit - will fill be exceeded

Conduit or direct burial - 18" or more deep

Detached building - requires a disconnect. Can be in the form of a main breaker. Main breaker can be larger than feed breaker. e.g. 60 feeder, 100 A main breakeri in garage.

NFPA 70/ NEC code - see the sticky how to read online for free. Registration required.

Wire - Copper or Aluminum

Load requirements - Only you can determine this. The maximum feeder breaker size is usually 100 A.

Ask a few questions based on these answers and I'll get back on wire size.

[dapixman]

#00 is OK for 100 amps at full load, the #6 copper is of no use except for a ground rod conductor for the service at the garage. Add a 100 amp breaker in your house service and run underground in PVC conduit with 3 runs or your #00. Add a new 100 amp panel in your garage with a main breaker and two ground rods minimum 6 feet apart connected with your copper line (make sere only one unbroken line connects to both rods)

[KISS]

#1 for L1 and L2, #6 grounding; assuming copper. The neutral size could be reduced with better analysis, otherwise #1.

1/0 or #0 for Aluminum and #6 grounding.

Both assume 70' and a 100 A breaker.

[tkrussell]

#2/0 for a 100 amp feeder?

#00 is OK for 100 amps at full load, the #6 copper is of no use except for a ground rod conductor for the service at the garage. Add a 100 amp breaker in your house service and run underground in PVC conduit with 3 runs or your #00. Add a new 100 amp panel in your garage with a main breaker and two ground rods minimum 6 feet apart connected with your copper line (make sere only one unbroken line connects to both rods)

I would say it is OK for 100 Amps, as #2/0 (AKA #00) is grossly oversized for a 100 Amp residential feeder.

#2/0 is good for a 150 Amp residential feeder.

#2/0 copper wire will not fit in a terminal on a 100 Amp breaker.


Only #4 copper or # 2 aluminum is needed for a 100 Amp RESIDENTIAL feeder.

So, 3 - #4 CU THWN plus 1 #8 CU THWN wire for the equipment ground is recommended for this feeder in 1 " Sch 40 PVC conduit minimum or larger.

Is anyone going to ask what size conduit has been purchased?

One should not buy conduit, then size the wire for who knows what size feeder.

Cart before the horse situation.


You also kind of limited yourself with wiring the garage with all #14 wire, as you are now limited to all 15 amp circuits.

[KISS]

Tk:

I was going to mention conduit size, but forgot.

Again, you calculated for <3% drop at 240v, whereas I calculated <3% drop at 120V. We don't know the neutral load and I think your calculations would be undersized if only one side of the box was used at 100 A of 120 V Volts.

Meaning, if you knew the number of 240 v devices, you could reduce the neutral current and neutral size that way.

e.g. If you had ten 240 V saws at 5 amps each, then you could size the neutral at 100-50 or 50 amps.

Otherwise, it makes sense that the legs be rated at their full potential which is 100 A at 120V.

There is no way to know the loads in this post and % on time, but at the same time in a one man shop, not all equipment will be used at the same time. With that argument, your calcs seem fair.

I recently saw an example problem on the NFPA website:

http://www.nfpa.org/assets/files/pdf/NecApD.pdf

Where leg 1, leg 2 and Neutral are calculated independently.

[stanfortyman]

I completely agree with TK's post. 2/0 for 100A, even at a measly 70 feet is absurd.

Again, you calculated for <3% drop at 240v, whereas I calculated <3% drop at 120V. We don't know the neutral load and I think your calculations would be undersized if only one side of the box was used at 100 A of 120 V Volts.

Meaning, if you knew the number of 240v devices, you could reduce the neutral current and neutral size that way.

With regard to this, I know I have stated this position before, but you DO NOT need to know the neutral load, or to know what the 240v loads/devices are. To say "what if only one side of the box is used" is like saying what if someone changed all the 20A breakers to 30's.
You DO NOT use 120v in figuring VD for a 120/240v FEEDER. You would have to INTENTIONALLY go out of your way to imbalance a single phase 120/240v panel. IE: Use only "one side".

I like that we agree on most things, but I have to part with you on this one. :D :cool:

[KISS]

You don't have to go out of your way. Just fill the panel with 100 A of loads using 120 V pieces of equipment on either leg.

[stanfortyman]

You don't have to go out of your way. Just fill the panel with 100 A of loads using 120 V pieces of equipment on either leg.

That's my point. You would have to intentionally skip breaker spaces.
You could fill one side of the panel and be balanced.

[tkrussell]

Oops, sorry, don't mean to be a smartass, but I did no calcs,

tk: With that argument, your calcs seem fair.

All of that is off the top of my head, sizing per code. The loads and distances did not concern me.

Wasn't complaining about you not mentioning conduit, but just a cute sarcastic way of pointing out of when not to buy conduit.

Stan and I have debated the voltage to use issue. I have never conceded, nor disagreed. Same as Vd correction is not required, but recommended, as is the voltage, more of a design choice, or judgment. Sometimes I use 120, sometimes assuming a much lower neutch current, sometimes just 240. Depends on conditions, loads, usage, distance.

With this senario, I see no problem with Vd. Heck, were not even sure what size feeder or circuit breaker Nate needs or wants.

Sorry Nate, us pros like to discuss, debate, and so on.

Nate, any more detail?

[KISS]

True. Nate may need a 60 A feeder. What nate got is 200 Amps of 120 V or 100 A at 240 V. 200(120) = 100(240) or 24 KVA of electricity using my calcs with a 3% drop.

He got the max (100 A) feeder because 100 A is the usual largest breaker available.

Nate may not need that and Nate may have to pick wires that will fit his purchased conduit and size a breaker accordingly.

[tkrussell]

Very true,

Nate may have to pick wires that will fit his purchased conduit and size a breaker accordingly.

Hopefully it is not in the ground and buried yet.

[NatePit09]

This is going to be a small furniture construction workshop, only basic hand power tools will be used. The biggest equipment I own and will be using would be a table saw or a band saw. I have the Sched 40 conduit already, but I haven't put it into the ground yet. I haven't purchased any breakers yet, I have been holding out to see what I would need to get to keep from tripping breakers while operating overhead lights and a few tools at once. I am running 5 separate circuits: 2 for lights in the separate sides, 2 for outlets in the separate sides, and 1 for outside lights on the front and back of the garage. The lighting is all plug in type shop lights and the outlets are duplex fixtures. I really do appreciate all of the help here, I have studied this stuff for the last couple of years and done most of it before, but this is the first time I have tackled a sub - panel installation by myself! So what size wire do I need to get to put it all together? Let me know what other info you guys need to know and I'll answer any question you may have. Thanks again! BTW: the Sched 40 conduit I have is 3/4" inside diameter.

[KISS]

SHould I tell him or should you. The max you can put in a 3/4 conduit is three #6's and one #8 also or four #6's.

[stanfortyman]

DO NOT use 3/4" !!

Use at least 1" or 1-1/4" (trade size) conduit.

Good thing it is not in the ground.

[tkrussell]

I would suggest, for several reasons, the 1-1/4" PVC conduit Stan suggests, and pull 3 - #2 Al XHHW and 1 - #6 Al XHHW. This is the most econmical, I think, and this will provide a 100 Amp service to the shop.

Allows for easy future expansion of operations in the garage.

A 100 A CB at the Main feeding this, a 100 Amp CB as a Main in the subpanel.

Need at least one ground rod grounding the equipment ground bar in the garage subpanel.

The neutral must be kept insulated and isolated in the subpanel, by not installing green screw or wire jumper labeled Main Bonding Jumper.

Ground bar may be a seaparate accessory.

Eventually you may need a 20 amp branch circuit in the garage, and that will need #12 wire/cable for that circuit. Any #14 can only be connected to a 15 amp branch circuit breaker, and you may have tripping issues with some tools/equipment.

If this is a commercial shop, and not just a residential hobby, may need to comply with OSHA and have GFI protection for any 15 or 20 amp receptacles, which would be a good idea even if this is for a hobby.

[Missouri Bound]

Suggestion. Bury the correct size conduit for your needs... and keep the 3/4" conduit.
You can bury it near, but not next to the proper size conduit and use it for security purposes, telephone line etc. Any low voltage applications. I don't know exactly how close you could put it, but if you use shielded low voltage wiring, the distance will be reduced.

[KISS]

6" is recommended for parallel runs.