Sizing copper grounding wire for 200A service

[Tinkerer]

I have a customer (my daughter actually) with a house, in southern Florida, built in the 50s. Her home inspection listed the ancient Zinsco service disconnect as a deficiency, and pointed out that the electrical panel grounds and neutrals are not isolated. There is 70 feet of 2" rigid pipe between the disconnect and the electrical panel. If I separate the grounds and neutrals, I will connect the neutrals to the neutral wire (correctly sized copper: good), and the grounds to the rigid pipe which is not bonded well to the boxes at either end (concentric knockouts: not-so-good). I think I can fish a new ground wire through the 70" of pipe, if it is not too big. NEC 250.66 Tells me I can use AWG 4 copper. I think I can fish this this through the 2" pipe. I don't usually do this calculation; normally I just use SER cable which has an AWG 2/0 aluminum (copper AWG 1 equivalent) ground. I wonder why SER cable has a ground which is so much larger.

Please tell me if I have thought through this situation correctly.

Doug

 

[letgomywago]

I have a customer (my daughter actually) with a house, in southern Florida, built in the 50s. Her home inspection listed the ancient Zinsco service disconnect as a deficiency, and pointed out that the electrical panel grounds and neutrals are not isolated. There is 70 feet of 2" rigid pipe between the disconnect and the electrical panel. If I separate the grounds and neutrals, I will connect the neutrals to the neutral wire (correctly sized copper: good), and the grounds to the rigid pipe which is not bonded well to the boxes at either end (concentric knockouts: not-so-good). I think I can fish a new ground wire through the 70" of pipe, if it is not too big. NEC 250.66 Tells me I can use AWG 4 copper. I think I can fish this this through the 2" pipe. I don't usually do this calculation; normally I just use SER cable which has an AWG 2/0 aluminum (copper AWG 1 equivalent) ground. I wonder why SER cable has a ground which is so much larger.

Please tell me if I have thought through this situation correctly.

Doug

You a licensed electrician in Florida? First disconnect has the main bonding jumper then is the separation. Home Inspectors call out the shared lugs of ground and neutral bars often. Or are you adding an outside disconnect because then you have other issues like the dryer and oven not being grounded by exception when going to the first disconnect.

 

[roger]

Tinkerer, please update your profile to show an accurate location and profession.

 

[roger]

Bump

 

[letgomywago]

OK to real advice I'd do a disconnect if needed and use ground bushings on the rigid. New circuits to dryer and oven or if needed run a 10awg ground to them if that's what is available from the water heater or something and fix the bond issue. Is Florida on the 2020 or 2017?

 

[Tinkerer]

Tinkerer, please update your profile to show an accurate location and profession.

Done

You a licensed electrician in Florida? First disconnect has the main bonding jumper then is the separation. Home Inspectors call out the shared lugs of ground and neutral bars often. Or are you adding an outside disconnect because then you have other issues like the dryer and oven not being grounded by exception when going to the first disconnect.

I am trying to keep these two issues separate.

1) The service conductors: As it is now much of the neutral current is returning to the meter through the steel of the rigid pipe. This seems like a bad idea to me, especially if the neutral ever becomes disconnected. I know there is a tiny chance of this, but she is my daughter and she has little children. My question is about the use of 4AWG copper service ground. I am sure this was on my Master electrician exam which I passed decades ago, but I just want to make sure, since I haven't needed to do these calculations recently. I also want to know why SER has such a large ground (probably not a code question).

2) The Zinsco service disconnect: The home inspector claims that Zinsco circuit breakers have a poor reputation and that many insurance companies refuse to insure homes with Zinsco breakers installed. A quick internet search tells me that there is some truth to this. A new service disconnect isn't expensive, and when I change it out, it is a good time to install bonding bushings.

Doug

 

[Tinkerer]

OK to real advice I'd do a disconnect if needed and use ground bushings on the rigid. New circuits to dryer and oven or if needed run a 10awg ground to them if that's what is available from the water heater or something and fix the bond issue. Is Florida on the 2020 or 2017?

There is no oven, drier, or range issue, I think

 

[letgomywago]

There is no oven, drier, or range issue, I think

So no electric dryer or range at all? 99% of old panels are older than 96 and are missing a ground wire because of the exception that allowed it so when you make that panel a subpanel with an outside disconnect then that is in violation of that original installations code exception and you have to fix it. Using rigid as an equipment ground is beaten dead horse and isn't an issue so long as the run isn't heavily coroded. The bare wire in SER is for use as a nuetral in 3phase since it's "Service" wire. We use it for single phase as a ground because we can and it works good for that.

 

[Sberry]

Some of the cables have larger ground because they are used where V drop is a concern.

 

[Tinkerer]

Florida is on 2017 NEC.

 

[letgomywago]

Zinsco work but are old obsolete and no options for afci and gfci so replacing them is common on home sales. I really think that you'll need to either redo it all or only redo the panel with existing meter staying the same being on the 17 allows that so if you can aim for that.

 

[Tinkerer]

So no electric dryer or range at all? 99% of old panels are older than 96 and are missing a ground wire because of the exception that allowed it so when you make that panel a subpanel with an outside disconnect then that is in violation of that original installations code exception and you have to fix it. Using rigid as an equipment ground is beaten dead horse and isn't an issue so long as the run isn't heavily coroded. The bare wire in SER is for use as a nuetral in 3phase since it's "Service" wire. We use it for single phase as a ground because we can and it works good for that.

letgomywago, Thanks, some good information here. 3-phase, it makes perfect sense, although don't you still need a ground? I am not sure what you mean about my beaten dead horse. I think you are saying that rigid pipe in good shape, with bonding bushings is still a suitable ground conductor. There is an new electric range (4-wire), and a electric drier (near the main panel). I think I am in good shape.

Doug

 

[Tinkerer]

Zinsco work but are old obsolete and no options for afci and gfci so replacing them is common on home sales. I really think that you'll need to either redo it all or only redo the panel with existing meter staying the same being on the 17 allows that so if you can aim for that.

What changes in 2020?

 

[tom baker]

In G&B it is very helpful to use the correct terms. Please look up the definition of ground. Or as Mike Holt once said, what color is it and what does it do?

 

[suemarkp]

A feeder ground uses table 250.122. Table 250.66 is only for the conductor to a ground electrode. Ground electrode should be at the service. Feeder EGC would be #6 copper.

 

[infinity]

Just my 2 cents but you need to rip out the Zinsco garbage and replace it. There's a reason that they went out of business and that's because their stuff is prone to failure or worse. The existing RMC raceway can be reused for the feeder to the panel. Might be good a idea to use bonding bushings if you feel that the original connection of the raceway is impaired but they're not required. If you want to use a wire type EGC you only need a #6 for a 200 amp feeder as suemarkp stated.

 

[Tinkerer]

I am totally going to replace the Zinsco breaker.

In G&B it is very helpful to use the correct terms. Please look up the definition of ground. Or as Mike Holt once said, what color is it and what does it do?

It is green or copper and it provides the fault path from the breaker panel back to the meter for any accidental equipment grounding event in the house.

Doug

 

[Tinkerer]

A feeder ground uses table 250.122. Table 250.66 is only for the conductor to a ground electrode. Ground electrode should be at the service. Feeder EGC would be #6 copper.

This makes sense.

 

[letgomywago]

I am totally going to replace the Zinsco breaker.



It is green or copper and it provides the fault path from the breaker panel back to the meter for any accidental equipment grounding event in the house.

Doug

Both equipment grounds and service grounded conductors can be bare and grounding electrode conductors can be green and bare like equipment grounds so you need to use the proper terms for each one.

Replacing it will trigger new grounding electrode system in most locations so you'll need to see what is required from the local Florida AHJ but most places will need interstyem bond and new rods or plates and new water bond if applicable with in 5 ft.

 

[Tinkerer]

Thanks!