Main Service Splitter Panel

[Mattlt]

My wife has given approval for me to build a dedicated woodworking shop! Now, I need to get power to it. My meter panel is about 275' away, and I have the pictured "splitter box" below my meter. This install was done in 1995.

The conduit in the middle feeds the house (200 amp service) and the one on the right feeds the current multi-purpose shop (100 amp service) My thought is to add another ~100 amp service for the woodworking shop. I'm thinking #2 aluminum... I realize that might be a little short for 100 amp, I'm OK with a little smaller if need be. Anyway, I digress.

Here's my question. The box only has three connection points, not four. I keep reading on this site about four wires being run to subpanels, 2008 code requiring four wires, etc. Where would I hook the 4th wire? Can I just run a three wire cable? (or three separate wires?)

Oh, note the bottom left connection, that's the neutral connection. The electrician that installed this seems to have "bonded" the neutral to the splitter box itself. (The bare wire behind the middle conduit) The box is not directly connected to a ground rod, although there is steel conduit connecting the panel to the meter box, up the weatherhead to the transformer. The transformer is connected to a ground wire running the length of the pole. So I guess in theory, everything is bonded togther.

Can I just run three wires and put a ground rod(s) at the new shed?

 

[Falcon67]

I'm not the electrician, but I think you'd have to do what I did - both your neutral and your ground will come off the lower left bus bar. And you'll still need the grounding system at your building - UFER, rods, both, what your AHJ says.

 

[pattenp]

I believe what you have is still considered a service entrance conductor point because this is straight off the meterbase with no up stream disconnecting means. So the runs from here are service entrance conductor feeds and only require 3 wire service cable to the panel in your house and shop. I'm not totally familiar with the set up but I'm sure someone else will correct me if I'm wrong. The four wire requirement is for feeders being supplied from a main service panel to an auxiliary panel (sub-panel). Your house and shop panels are considered main service panels and any panel fed from those would be sub-panels and would require the four wire feeder. The new shop will require ground rods. I hope this makes sense.

 

[Mattlt]

I believe what you have is still considered a service point because this is straight off the meterbase with no up stream disconnecting means. So the runs from here are service feeds and only require 3 wire service cable to the panel in your house and shop. I'm not totally familiar with the set up but I'm sure someone else will correct me if I'm wrong. The four wire requirement is for feeders being supplied from a main service panel to an auxiliary panel (sub-panel). Your house and shop panels are considered main service panels and any panel fed from those would be sub-panels and would require the four wire feeder. The new shop will require ground rods. I hope this makes sense.

I like this answer! Thanks.

 

[pattenp]

As I said before, I think I'm correct on this and no one else has said anything to the contrary. Also, being a 3 wire service entrance feed, #2 aluminum is good for 100A.

 

[Aceman]

As I said before, I think I'm correct on this and no one else has said anything to the contrary. Also, being a 3 wire service entrance feed, #2 aluminum is good for 100A.

He's feeding a shop, not a dwelling. That makes #2 AL still 90 amp wire, not 100. But everything else you've said is right on track.

The install is before the first disconnecting means, which is where you're grounding electrode is installed, and 4 wire feeders start. So it is OK to run a 3 wire feed to your workshop. Drive rods/ufer, etc, bond the neutral/ground and so on. It's a main service panel, so you treat it as such.

I would advise you to have a load calc done before adding a third load to those existing meterbase wires. Chances are you'll be alright, but there's no way of knowing without a calc.

 

[pattenp]

Thanks Aceman for that correction. 310.15 (7) does say only dwellings. I really don't understand in this situation why code limits this to dwellings only. I knew someone would correct me me if I stated something incorrectly.

He's feeding a shop, not a dwelling. That makes #2 AL still 90 amp wire, not 100. But everything else you've said is right on track.

The install is before the first disconnecting means, which is where you're grounding electrode is installed, and 4 wire feeders start. So it is OK to run a 3 wire feed to your workshop. Drive rods/ufer, etc, bond the neutral/ground and so on. It's a main service panel, so you treat it as such.

I would advise you to have a load calc done before adding a third load to those existing meterbase wires. Chances are you'll be alright, but there's no way of knowing without a calc.

 

[Mattlt]

So that means I would need a 90 amp breaker in the panel in the workshop? Not a 100 amp breaker?

The panel in my current shop has a 100 amp breaker. Change in code since 1995? Now, the current shop is < 100' away from the the main. The new one will be about 275' away. If that matters.

Thanks for the advice!

 

[pattenp]

90A breaker is what you need on #2 Al. You need to do a voltage drop calculation because 275' is a long run for #2 at 90A. Are you doing conduit or direct bury?

 

[theoldwizard1]

90A breaker is what you need on #2 Al. You need to do a voltage drop calculation because 275' is a long run for #2 at 90A. Are you doing conduit or direct bury?

According to this on line calculator, #2 Al @90A will give you a 6.5% (15.5V) drop. You have to go to 0 AWG (Al) to get less than a 5% drop @90A.

#2 Al will have less than a 5% drop @275' at 80A or less.

 

[pattenp]

Did you mean 2/0?

According to this on line calculator, #2 Al @90A will give you a 6.5% (15.5V) drop. You have to go to 0 AWG (Al) to get less than a 5% drop @90A.

#2 Al will have less than a 5% drop @275' at 80A or less.