Wire Size for 400 amp service

[brad225]

New to the Forum, thanks to Mike and all that make it possible.

I live in Florida and had the local electrical company here this week to put in underground service to a new pole barn I am building on our property. It will have a 200 amp service and they ran 4/0 Aluminum 269' from the transformer that was set 3 years ago when we renovated our house.

My question relates to the wire size they ran to the house during the renovation that has a 400 amp meter socket and 2-200 amp panels. When I was watching them pull the wire into the transformer ( this week for the pole barn ) I noticed that the wire size that ran to the house was smaller than the 4/0 they had just pulled to the pole barn. Shouldn't it be at least 4/0 maybe larger for the 400 amp service?

This may also be the answer to an issue we have had since the completion of the house. When either of the air conditioners start up the lights in the house dim for a moment. This is particular annoying since I asked my electrician to up the wire size for any lighting circuit to #12 to avoid this happening. I have had 2 other HVAC companies check the units and both said they were fine and wired with the proper size wire.

My guess at this point is that even though you get an acceptable voltage reading when checking any wire the voltage drop under startup load is to much for the wire from the transformer to the meter socket. The entrance cable to both panels is 4/0 aluminum. One has a run of 8' and the other has a run of 30' to the automatic transfer switch for a future generator and then 30' to the second panel.

I'm I thinking in the right direction or am I missing something.


Thanks Brad

 

[Dennis Alwon]

We have no control over what the power company does but they are responsible to provide adequate power to the building. IMO, they ran a very small wire for the size of the service and the distance. Of course service size doesn't necessarily mean much it is the load that counts.

There is no NEC rule that can be used to fight the power company but I certainly would approach them with the issue you are having

 

[GoldDigger]

I have one comment on your general understanding of the problem:
It is not voltage drop itself that causes the noticeable problem, it is the difference in voltage drop when the current through the wire changes.
So putting in #12 to the lights will not help you, since the varying voltage is at the supply end of those wires and any voltage drop in the #12 will be constant whenever the lights are on.
You need to concentrate on those parts of the path where the lighting current and the A/C current travel over the same wires.
That means the wiring from the utility to your panel and any wiring from your main panel to a subpanel that supplies both A/C and lights.
You should be able to measure the voltage drop where the utility wires come into the first box that you have access to. If there is a large voltage drop there when the A/C turns on, then the utility wiring is undersized. Whether they will correct it or not is another question.

 

[don_resqcapt19]

Most state utility commissions have rules on "excessive" flicker, but I am not sure if you really have "excessive" flicker. The issue can be the voltage drop in the service conductors and/or the voltage drop in the transformer itself.

 

[edlee]

New to the Forum, thanks to Mike and all that make it possible.

I live in Florida and had the local electrical company here this week to put in underground service to a new pole barn I am building on our property. It will have a 200 amp service and they ran 4/0 Aluminum 269' from the transformer that was set 3 years ago when we renovated our house.

My question relates to the wire size they ran to the house during the renovation that has a 400 amp meter socket and 2-200 amp panels. When I was watching them pull the wire into the transformer ( this week for the pole barn ) I noticed that the wire size that ran to the house was smaller than the 4/0 they had just pulled to the pole barn. Shouldn't it be at least 4/0 maybe larger for the 400 amp service?

This may also be the answer to an issue we have had since the completion of the house. When either of the air conditioners start up the lights in the house dim for a moment. This is particular annoying since I asked my electrician to up the wire size for any lighting circuit to #12 to avoid this happening. I have had 2 other HVAC companies check the units and both said they were fine and wired with the proper size wire.

My guess at this point is that even though you get an acceptable voltage reading when checking any wire the voltage drop under startup load is to much for the wire from the transformer to the meter socket. The entrance cable to both panels is 4/0 aluminum. One has a run of 8' and the other has a run of 30' to the automatic transfer switch for a future generator and then 30' to the second panel.

I'm I thinking in the right direction or am I missing something.


Thanks Brad

In my experience the lights will always dim for a moment when a load like the AC starts up.

The question is, how severe is the dimming and how long does it last? If there is a problem with voltage drop then the AC compressor will have trouble starting. If the compressor(s) start up smoothly and the lights dip briefly then I think everything is likely working as it should.

 

[brad225]

Thanks for all of the responses and information. I have called an electrician to make the final connections in the meter socket and main panel of the pole barn. I will ask him if we can check the voltage drop in the main panels when he is here for the other work.

Our power company Withlacoochee River Electrical Cooperative is very easy to work with. Once I have more information from the electrician I can talk to WREC engineers I have worked previously.

I will post the results of the testing.