200 Amp Main Install

[jaw22w]

I am just about to start the electrical installation in my new pole barn. I have a few questions.
When we built the house 5 years ago, we put in a 400-amp box just after the transformer. There is one 400 main breaker and two 200-amp secondary breakers. One side (200-amps) goes to the house. Now the other side (200-amps) will power the new shop. The new circuit to the shop will require 90 feet of service entrance cable to a 200-amp main breaker in the shop.
Through my research, I believe that a 4/0-4/0-2/0 direct burial aluminum wire is what I need. Is that correct?
I have a Square D Homeline 200 Amp, 30 circuit main box. Can this box be installed upside down? What I mean is, I want the power to come in the bottom of the box and not have to snake around to the top of the box. So, the 200-amp main breaker would be at the bottom of the box instead of the top. Would this be legal?
Last question (for now). There are 2 ground rods at the 400 amp box. Do I need another ground rod at the main breaker in the shop?
Obviously, I am not an electrician. I am pretty comfortable with wiring from the main breaker on, but don't have much experience with service entrance work. I think it should be pretty straight forward. I guess the most important thing will be to make sure the main 400-amp breaker is pulled before any work inside the box!
Thanks for any answers, tips or tricks.

 

[Jim greengo]

I've seen plenty of them mounted that way,just remember you'll need a 4 wire feed for it.

 

[beemerphile]

The new circuit to the shop will require 90 feet of service entrance cable to a 200-amp main breaker in the shop.

It would be a 4-wire feeder cable and not a 3-wire service entrance cable.

Through my research, I believe that a 4/0-4/0-2/0 direct burial aluminum wire is what I need. Is that correct?

4/0-4/0-4/0-2/0 MHF

I have a Square D Homeline 200 Amp, 30 circuit main box. Can this box be installed upside down? What I mean is, I want the power to come in the bottom of the box and not have to snake around to the top of the box. So, the 200-amp main breaker would be at the bottom of the box instead of the top. Would this be legal?

Yes

Last question (for now). There are 2 ground rods at the 400 amp box. Do I need another ground rod at the main breaker in the shop?

Yes

 

[sparky 1971]

I am just about to start the electrical installation in my new pole barn. I have a few questions.
When we built the house 5 years ago, we put in a 400-amp box just after the transformer. There is one 400 main breaker and two 200-amp secondary breakers. One side (200-amps) goes to the house. Now the other side (200-amps) will power the new shop. The new circuit to the shop will require 90 feet of service entrance cable to a 200-amp main breaker in the shop.
Through my research, I believe that a 4/0-4/0-2/0 direct burial aluminum wire is what I need. Is that correct?

Check with the inspector. Some places, like where I am, will let you get away with it but, officially, you are on the wrong side of the main and it's supposed to be 250-250-3/0 and have a #6 copper or #4 aluminum grounding conductor. If those conductors are going to enter the building, make sure they are dual rated for indoor use. Straight URD can't be inside a building, but all of the supply houses I deal with carry the dual rated only.

I have a Square D Homeline 200 Amp, 30 circuit main box. Can this box be installed upside down? What I mean is, I want the power to come in the bottom of the box and not have to snake around to the top of the box. So, the 200-amp main breaker would be at the bottom of the box instead of the top. Would this be legal?

As long as the main breaker handle works horizontally and not vertically, there is no such thing as upside down. Top fed and bottom fed and I'm sure the panel is new enough that you will be ok.

Last question (for now). There are 2 ground rods at the 400 amp box. Do I need another ground rod at the main breaker in the shop?
Obviously, I am not an electrician. I am pretty comfortable with wiring from the main breaker on, but don't have much experience with service entrance work. I think it should be pretty straight forward. I guess the most important thing will be to make sure the main 400-amp breaker is pulled before any work inside the box!
Thanks for any answers, tips or tricks.

Yes, you will need two ground rods at the building, at least 6' apart tied together and to the panel. Someone is sure to chime in to tell you that if you can prove less than 25 ohms, only one rod is needed, but it's easier to plant two rods than buy a $2000.00+ meter.

 

[wyliesdiesels]

I am just about to start the electrical installation in my new pole barn. I have a few questions.
When we built the house 5 years ago, we put in a 400-amp box just after the transformer. There is one 400 main breaker and two 200-amp secondary breakers. One side (200-amps) goes to the house. Now the other side (200-amps) will power the new shop. The new circuit to the shop will require 90 feet of service entrance cable to a 200-amp main breaker in the shop.
Through my research, I believe that a 4/0-4/0-2/0 direct burial aluminum wire is what I need. Is that correct?

not correct. you need 4-wire feeder

second, do you really need 200a in the shop? what loads will you have? how many people? im guessing 90a may suit you well and thus you can downsize the wire...

I have a Square D Homeline 200 Amp, 30 circuit main box. Can this box be installed upside down? What I mean is, I want the power to come in the bottom of the box and not have to snake around to the top of the box. So, the 200-amp main breaker would be at the bottom of the box instead of the top. Would this be legal?

yes there is no up or down on new panels.

Last question (for now). There are 2 ground rods at the 400 amp box. Do I need another ground rod at the main breaker in the shop?

yes 2 rods are required at every structure

Obviously, I am not an electrician. I am pretty comfortable with wiring from the main breaker on, but don't have much experience with service entrance work. I think it should be pretty straight forward. I guess the most important thing will be to make sure the main 400-amp breaker is pulled before any work inside the box!
Thanks for any answers, tips or tricks.

if you have 200a breakers feeding the feeder circuits then there is no need to shut off the main 400a breaker..

 

[jaw22w]

It would be a 4-wire feeder cable and not a 3-wire service entrance cable.

4/0-4/0-4/0-2/0 MHF

I'm pretty sure that the house was only 3 wire, 4/0 4/0 2/0. I'm not qualified to argue, but why do I need the 3rd 4/0 wire?

 

[sparky 1971]

I'm pretty sure that the house was only 3 wire, 4/0 4/0 2/0. I'm not qualified to argue, but why do I need the 3rd 4/0 wire?

Pre 2008 code cycle three wire was acceptable. You don't need a third 4/0. If using 4/0, it would be two 4/0 hot conductors, a 2/0 neutral and a #4 ground, but since it's being used as a feeder instead of service entrance conductors, 4/0 may not cut it.

 

[mike93lx]

I'm pretty sure that the house was only 3 wire, 4/0 4/0 2/0. I'm not qualified to argue, but why do I need the 3rd 4/0 wire?

3 wire is fine between the meter and first means of disconnect. After that, it's 4 wire

 

[beemerphile]

Buy the new panel with a 150 main and 4/0 will be fine. Absent unusual equipment it would be unusual to need the 200 for a home shop.

 

[jaw22w]

Well, I took the cover off the 400-amp box this morning. I thought I had it all figured out where the 3 wires would go. I'm not sure there is a lug for the 3rd 4/0 wire.
I think you guys have convinced me to run the trench and call my electrician to power to the new pole barn

 

[sparky 1971]

Well, I took the cover off the 400-amp box this morning. I thought I had it all figured out where the 3 wires would go. I'm not sure there is a lug for the 3rd 4/0 wire.
I think you guys have convinced me to run the trench and call my electrician to power to the new pole barn

There isn't a third 4/0 wire. The grounding conductor will be a #4, as in 4awg. Seven sizes smaller than 4/0. #4, #3, #2, #1, 1/0, 2/0, 3/0, and finally, 4/0. The #4 will land on the neutral/ground bar in the meter/main. Probably a good call to have it done.

 

[beemerphile]

There isn't a third 4/0 wire. The grounding conductor will be a #4, as in 4awg. Seven sizes smaller than 4/0. #4, #3, #2, #1, 1/0, 2/0, 3/0, and finally, 4/0. The #4 will land on the neutral/ground bar in the meter/main. Probably a good call to have it done.

With a center tapped 240/120v service, how do you handle unbalanced neutral current with two 4/0’s and a grounded #4? The two underground services on my property bring three equal size conductors from the transformer. The one aerial service I have uses the messenger as the grounded neutral. I run three equal size conductors from the meter base to my service disconnect where the neutral is bonded to the driven grounds with a #4 GEC. From the load side of the service disconnect it is 4 wire.

What am I missing?

 

[mm08822]

Check with the inspector. Some places, like where I am, will let you get away with it but, officially, you are on the wrong side of the main and it's supposed to be 250-250-3/0 and have a #6 copper or #4 aluminum grounding conductor. If those conductors are going to enter the building, make sure they are dual rated for indoor use. Straight URD can't be inside a building, but all of the supply houses I deal with carry the dual rated only.

Op, definitely check with the inspector first (even if someone does the work). The exception in the code for reduced service entrance conductor size only applies to residential service conductors.
You are planning:

• a feeder to the barn
• the barn is not considered a residential dwelling.

With a center tapped 240/120v service, how do you handle unbalanced neutral current with two 4/0’s and a grounded #4? The two underground services on my property bring three equal size conductors from the transformer. The one aerial service I have uses the messenger as the grounded neutral. I run three equal size conductors from the meter base to my service disconnect where the neutral is bonded to the driven grounds with a #4 GEC. From the load side of the service disconnect it is 4 wire.

What am I missing?

The equipment grounding conductor, only used to trip the upstream cb in the even of a fault.
The grounded conductor is the neutral and it carries the imbalance between the 2 phase conductors.

At the point of service disconnect, the grounded conductor from the POCO transformer connects to the neutral bar and Is bonded to the equipment ground (at this location once and only once) and also connects to the equipment grounding electrode system.
From this point onward, the grounded conductor (Neutral) is run independently and isolated from the equipment grounding conductor (bare/green).

This separation of grounded/grounding conductors is done for safety reasons so the egc only carries incidental fault current.

 

[beemerphile]

…The equipment grounding conductor, only used to trip the upstream cb in the even of a fault.
The grounded conductor is the neutral and it carries the imbalance between the 2 phase conductors.

At the point of service disconnect, the grounded conductor from the POCO transformer connects to the neutral bar and Is bonded to the equipment ground (at this location once and only once) and also connects to the equipment grounding electrode system.
From this point onward, the grounded conductor (Neutral) is run independently and isolated from the equipment grounding conductor (bare/green).

This separation of grounded/grounding conductors is done for safety reasons so the egc only carries incidental fault current.

I understand all that. The current carrying grounded conductor is what seems to be missing from Sparky’s description of a service composed of two 4/0’s and a #4 grounding conductor.

 

[mcbane]

250 wire probably only needed if your calculated loads are over 180A. Last time I installed a garage feeders my loads were calced at 180 A total and it was ok to use a 200A breaker and 4/0 current carrying conductors. Obviously best to check with AHJ before buying your wire.

 

[sparky 1971]

With a center tapped 240/120v service, how do you handle unbalanced neutral current with two 4/0’s and a grounded #4? The two underground services on my property bring three equal size conductors from the transformer. The one aerial service I have uses the messenger as the grounded neutral. I run three equal size conductors from the meter base to my service disconnect where the neutral is bonded to the driven grounds with a #4 GEC. From the load side of the service disconnect it is 4 wire.

What am I missing?

It's two 4/0, one 2/0, and a #4 grounding conductor. The point is that there aren't three 4/0 wires. He was trying to figure out where to put the third 4/0 wire.

 

[sparky 1971]

I understand all that. The current carrying grounded conductor is what seems to be missing from Sparky’s description of a service composed of two 4/0’s and a #4 grounding conductor.

Where did a three wire service get described?

You need to go back and read my post in #4, then #7. Then and only then can you get the context of my post in #11. Then when you read #11, take note that I specifically stated grounding conductor, not grounded.

 

[beemerphile]

You need to go back and read my post in #4, then #7. Then and only then can you get the context of my post in #11.

I musta took a left turn at Albuquerque. I don't downsize the neutrals in my feeders because it meets the worst case load imbalance with nothing to calculate per 220.61. In the 4/0 example, where I buy MHF, 4/0-4/0-4/0-2/0 is currently $9.72 per foot and 4/0-4/0-2/0-4 is $9.29. I'll spend the extra $0.43. I understand that a professional electrician would take what the Code allows, if nothing else because he is competing against other electricians who will also bid on that basis. I confused @jaw22w with my mention of a 4/0 neutral instead of the 2/0.

Sorry. My bad.

 

[sparky 1971]

I musta took a left turn at Albuquerque. I don't downsize the neutrals in my feeders because it meets the worst case load imbalance with nothing to calculate per 220.61. In the 4/0 example, where I buy MHF, 4/0-4/0-4/0-2/0 is currently $9.72 per foot and 4/0-4/0-2/0-4 is $9.29. I'll spend the extra $0.43. I understand that a professional electrician would take what the Code allows, if nothing else because he is competing against other electricians who will also bid on that basis. I confused @jaw22w with my mention of a 4/0 neutral instead of the 2/0.

Sorry. My bad.

The neutral is automatically downsized with URD and most of the time with MHF. I won't use that MHF because of the ground. The MHF I use is 4/0-4/0-2/0-#4

 

[wyliesdiesels]

Highly unusual and rare that you would be able to overload a reduced size neutral...

 

[mike93lx]

Highly unusual and rare that you would be able to overload a reduced size neutral...

Let alone a 2/0 neutral. I don't believe I could intentionally do that

 

[beemerphile]

A "too large" wire only means reduced voltage drop and some extra expense. In 1937 NEC Section 90-1 read...

"The requirements of this Code constitute a minimum standard. Compliance therewith and proper maintenance will result in an installation reasonably free from hazard but not necessarily efficient or convenient. This Code is to be regarded neither as a design specification nor an instruction manual for untrained persons. Good service and satisfactory results will often require larger sizes of wire, more branch circuits, and better types of equipment than the minimum which is here specified.”

So if over-sizing a neutral is a sin, it is a venial one.