Square D Q0 200A Panel - how to convert to sub panel (separate neutral / ground bars)

farmer2009 · Sep 2, 2015

One question about your service feed. Are you sure it's a 400amp feed?

Here 400amp requires 2-3" conduits and a non-bypass meter. Then the power company feeds 6 wires not 3. Your side of the meter is wired true 400. But the power company here calls what you have 320 amp service. As its a single feed with a bypass meter. (The red handle).

pclausen · Sep 2, 2015

No I'm not sure. I just assumed that since it is feeding 2 200A panels, it would be rated at 400A. But you're probably right that it's a 320A base.

farmer2009 · Sep 2, 2015

Might be something to check out. Melted service is no fun. I melted out a setup just like yours last fall. About 170 amp continuous demand. Power company put everything on their side back like it was only made me install a non bypass meter base. Then as they were pulling out said "we'll be back in 10 years to replace it ". Made me feel real good. My meter was melted bad enough that you could get two fingers in beside cover.

The oxidation paste is code on all aluminum wire here. Inspector will fail over it.

pclausen · Sep 2, 2015

Just to be clear, the 320A meter base has been on the house since it was built back in the 80's. As has the two 200A breaker panels. All I did was to add a transfer switch in the feeder loop to one of those 2 panels, using 3/0 copper wire, rated for 200A.

The 36KW diesel generator will be able to supply 150A @ 240 volt, and has a 150A breaker on it. I know code requires that the feeder wires from the generator to transfer switch should be sized 15% above the capacity of the generator. So 150A + 15% = 176A. I plan to use the same 3/0 copper wire as everywhere else, so that should be plenty of margin.

While the 3 HVAC systems are all connected to the panel on generator power, I don't think they will be able to pull more than 150A with all 3 running at the same time.

2 units were replaced about 10 years ago, and the 3rd one just last year. I believe they are sized as follows:

Main unit 6 ton with 15KW aux heat
2nd floor unit 4 ton with 10KW aux heat
Master suite 3 ton with 6KW aux heat

All the systems are single stage heat pump. I guess if all 3 were to go into defrost at the same time during the winter during very cold condition while running on generator power, it might trip the 150A breaker at the generator.

I'll pick up some more oxidation paste and hit those 2 aluminum grounds in the panel with them.

Would an inspector also look at the existing wiring in panel 1, which I didn't touch, and fail it due to there not being any paste on those wires either?

What about the meter base with the utility lines coming in. They don't have paste on them either from what I can tell, so does the existing feeder to the panel I didn't touch.

I was planning to call the power company and have them come out and put a new seal on the meter base after inspecting my work there. This way it will be sealed when the county inspector gets here. I'm not sure how the county inspector would reach if there was no seal on the meter base when he comes to inspect. On the other hand, maybe he wants to inspect the work inside the meter base and I should not call the power company until after the county inspector has been out?

buickanddeere · Sep 2, 2015

I have not read all the way through but........... There is only supposed to be one location at the first service where the neutral system is bonded to ground, to hold the ground system to near true earth potential.
As previously stated the ground system is for grounding, not for carrying neutral current. That is why line and neutral load carrying conductors are insulated and the ground is often bare. If the ground and neutral system were the "same", then why does the NEC spec a separate ground and neutral system?
The ground system has one and only one use. That is to hold anything it is connected to, to near earth potential. That is it. No carrying of "normal" load current. Anybody thinking otherwise needs to better understand electrical services.
Yes I know back in the bad old days there were some ugly ground/neutral designs that are still in service now that should have never existed. non polarized plugs too. Clothes dryers come to mind. Hence stories about getting shocks from plumbing and appliances.
The transfer switch and generator have to match. A two pole transfer switch is fine if the generator is not bonded. If the generator is bonded then a three pole transfer switch that also transfers the neutral is required.
There should be two 10ft ground rods driven 10 or more feet apart and bonded back to the panels with #6 or #3 copper depending on where in the system.

hr3 · Sep 2, 2015

pclausen said:
It was a huge pain. My original plan was to route the 3/0 copper through the opening between the meter base the the right panel. But once I got the old feeder removed from the meter base, I realized there was no conduit in the wall between the meter base and panel on the inside. So I then had to unbolt the inside panel as was the bared able to get to the set screws on the 2" clamp on the back. Once I got that loose, I was able to pull the old feeder through from the inside. I was lucky that the clamp on the meter base was not tight and I was able to pull the feeder through, although I had to pull on it hard to get it to go. Once I got it out, I mounted the panel to the wall again and installed a 2" plug in the hole.

I thought about installing a 2" conduit pipe in the wall between the meter base and panel, but after pulling out the old feeder, I realized that the existing hole was not 2" diameter but rather 3 smaller holes drilled next to each other, just large enough for that original feeder wire. So I had to get rent a core bit and drill and drilled a 2 5/8" hole in a new location, and then installed my 2" conduit for the new feeder wires to run through.

What a pita that must have been. But you did it right at least ..

pclausen · Sep 2, 2015

Ok, so here's a crude wiring diagram of how everything is wired (except the generator which is not here yet):

We have the 2 grounding rods at the bottom coming up into the meter base. Just prior to entering, there's a join to the ground going to the transfer switch.

The utility lines are shown entering the meter base from below. The wiring to the left panel is all original and you can see how neutral and ground are bonded in that panel.

Also coming out of the meter base is the feed to the transfer switch. You can see how ground is bonded to neutral in the transfer switch and are run separately to the 2nd panel where they are not bonded.

Generator does not have its own grounding rod since it is grounded via the meter base.

Anything not look right to you guys that the inspector is going to call me on?

Also, do I need to dig up and expose the grounding rods for the inspector? I hope not as that would be a complete pain.

p.s. I'm not showing the close to run control wires that will run between the transfer switch and generator for auto start. Those control wires will be run in a separate conduit from the feed wires.

pclausen · Sep 2, 2015

buickanddeere said:
There is only supposed to be one location at the first service where the neutral system is bonded to ground, to hold the ground system to near true earth potential.

Given that this install is a "hybrid" of sort, with one of the original panels having bonded neutral and ground in it, and the other panel now being a sub-panel, does this still hold true?

In other words, am I forced to basically make the the 2nd panel a sub panel as well and ground everything in the transfer switch? I sure hope not.

s219 · Sep 2, 2015

pclausen said:
I know code requires that the feeder wires from the generator to transfer switch should be sized 15% above the capacity of the generator. So 150A + 15% = 176A. I plan to use the same 3/0 copper wire as everywhere else, so that should be plenty of margin.

The 115% conductor ampacity requirement is only applicable when the only breaker is at the end of the wiring run. But almost all generators/installs I have seen have a breaker on the generator (or as close as possible), at the beginning of the wiring run. In that case, your wire can be sized for the actual load.