Main Disconect to Main Lug Distance

[sands35]

The main disconnect for my house is on the south wall the basement.

Two main lug panels are on the north wall, ~25 feet away.

The disconnect to lug #2 and #3 is line of sight and direct walking path from disconnects.

Backstory:
I am collecting parts and making plans to re-wire the 2nd floor with a sub-panel. 60 year old house with mostly original tar paper wrapped wire without ground. Multiple dead outlets in house and a few that have bad voltage readings.

I'm pretty sure the AHJ is going to ask me to re-wire from the disconnect to the main lug panel. Multiple previous owners and not sure who did what when, but the wire is 1/0 copper and 2/0 is required under 310.16 note 5 (as I read it). The ground wire looks like 4 or 3 copper, not 1/0 copper (can step down 1 size for ground?). (all the wire is old and I can't make out gauge printing on it)

In prior work with the AHJ he likes to bring stuff up to code if it relates to a remodel, so it might have been OK 20 years ago, but not now. The dude will quote me back NEC code sections if I ask a question (rather than give me solutions), so I'm educating myself prior to asking him.

Questions:
1) Is 25' OK to not have a main disconnect on the panel? (then I don't need to buy a new panel - there are 2, one is full and 1 is unused at the moment)

2) Is 2/0 copper or 4/0 AL OK for the feeder? (I'll likely use SER if need to change)

3) Ground is bonded in the main disconnects - so separate ground from neutral in the main lug regardless of the disconnect in the panel?

Main Disconnects (#1,2,3) (main lug for the majority of the house is in the corner - panel is full so need to use the second panel



Main Lug #2 and #3 (yes, I need to tape down the labels "properly" )

 

[wyliesdiesels]

The main disconnect for my house is on the south wall the basement.

Two main lug panels are on the north wall, ~25 feet away.

The disconnect to lug #2 and #3 is line of sight and direct walking path from disconnects.

Backstory:
I am collecting parts and making plans to re-wire the 2nd floor with a sub-panel. 60 year old house with mostly original tar paper wrapped wire without ground. Multiple dead outlets in house and a few that have bad voltage readings.

I'm pretty sure the AHJ is going to ask me to re-wire from the disconnect to the main lug panel. Multiple previous owners and not sure who did what when, but the wire is 1/0 copper and 2/0 is required under 310.16 note 5 (as I read it). The ground wire looks like 4 or 3 copper, not 1/0 copper (can step down 1 size for ground?). (all the wire is old and I can't make out gauge printing on it)

In prior work with the AHJ he likes to bring stuff up to code if it relates to a remodel, so it might have been OK 20 years ago, but not now. The dude will quote me back NEC code sections if I ask a question (rather than give me solutions), so I'm educating myself prior to asking him.

Questions:
1) Is 25' OK to not have a main disconnect on the panel? (then I don't need to buy a new panel - there are 2, one is full and 1 is unused at the moment)

2) Is 2/0 copper or 4/0 AL OK for the feeder? (I'll likely use SER if need to change)

3) Ground is bonded in the main disconnects - so separate ground from neutral in the main lug regardless of the disconnect in the panel?

Ok lot to go over here.

I will address the stuff I bolded in your quote.

First off, which code cycle are u on? T310.16 is old. The new table is 310.15(b)(16).

How many amps is the disconnect or breaker? without knowing the breaker or fuse size, we cant tell u if 1/0 or 2/0 is the right size.

The same goes for sizing EGCs/grounds. Need to know protection size. Lookup T250.122 for EGC sizing.

Questions:

1) a panel does NOT need a main disconnect if it is in the same building as the main service disconnect. So u should be good.

2) As said above, we need to know the protection size before advising of proper wire size. Yes i would use SER!

3) the neutral is suppose to be bonded at the main service panel. In your situation, it sounds like u have a divorced meter(meter pan) and multiple main disconnects with the neutral bonded in all 3? It should probably be bonded in one main spot but your setup is probably fine. Yes, neutral bonding points PAST all of the main disconnects should be removed and the neutral bars need to be checked for isolation. If EGCs are terminated on any of the neutral bars in any of the main lug panels, they need to be moved to a ground bar that is bonded to the panel. Ground bar kits can be purchased to do this.

Another thing. If u DO have bonded neutral bars in any of the main lug panels, then that means u have 3 wire feeders between the disconnects and main lug panels. This means that either an EGC needs to be added, if individual conductors were used, or IF a jacketed type cable such as SEU was used then a whole new cable assembly such as SER will need to be ran from the disconnects to the main lug panels.

(One of the other sparkys would be able to better advise u on bonding with multiple main disconnects as Ive not had to deal with that before. Out here in Cali, most service mains are installed with a combo panel on the outside with a bonded neutral.)

Good luck. Sounds like youve got your work cut out for u.

One last thing. If u DO have 3-wire feeders, do the right thing and upgrade them to 4-wire. Its safer and 3-wire feeders to panels in the same building as the main service were never allowed as far as i know.

 

[sands35]

Thanks for the clarification on the disconnect distance.

200 amp fuses in each main disconnect. 1 for each main line - Sorry - should have listed that.

I looked at down rating the fuses to 150 or 100 amps, but the stupid adapters would cost more than re-wiring it.

Currently it is 3 wires (2 hots, 1 ground/neutral, THHN near as I can tell) from the main disconnect to each of the 2 main lug panels. The conduit is metal though. I haven't looked to see if the ground/neutral is bonded in the main lugs though. Will do that tonight.

 

[wyliesdiesels]

Earlier u mentioned 1/0 and 2/0 cu THHN.

For 200a, u actually need 3/0 CU or 250Kcmil AL. 3/0 CU SER is gonna cost some SERIOUS bucks!

Im guessing u were reading T310.15(b)(7) which is for 3-wire main service entrance wire. Your wire, while only 3-wire feed, doesnt qualify and shouldve been 4-wire due to the disconnects. Your wire, since its AFTER the first disconnect, doesnt qualify to be sized by T310.15(b)(7), which BTW, has been removed from NEC 2014 code cycle.

Since its all metal conduit, then just isolate the neutral bars and add a ground bar.

Move EGCs over to new ground bar.

 

[sands35]

ok - thanks!

I might have to put in a 125 or 150 amp main panel to control cost on the feed wire from the disconnect the panels. I'll have to think on that one. I don't need 200 amps in those 2 sub panels. There's a handful of light circuits and the house AC units. 100 amps should be enough.

3/0 copper is $3.09 a foot, 30 feet with 3 conductors, then a ground - conduit is 1.25" so too small for fill.

I'll have to call around for a price on 250 kcml AL wire, not at the big box places locally.

I need to be looking at the 75*C column? 4/0 SER AL isn't rated to 200 amps that way?

 

[wyliesdiesels]

ok - thanks!

I might have to put in a 125 or 150 amp main panel to control cost on the feed wire from the disconnect the panels. I'll have to think on that one. I don't need 200 amps in those 2 sub panels. There's a handful of light circuits and the house AC units. 100 amps should be enough.

3/0 copper is $3.09 a foot, 30 feet with 3 conductors, then a ground - conduit is 1.25" so too small for fill.

I'll have to call around for a price on 250 kcml AL wire, not at the big box places locally.

I need to be looking at the 75*C column? 4/0 SER AL isn't rated to 200 amps that way?

yes use the 75* column as long as every termination point is rated at 75* c otherwise, u have to use the 60* c column.

And I wasnt thinking earlier about the use of smaller AL wire:

A look at 240.6(a) shows that 180a is NOT a standard fuse or breaker size, so youre allowed to go to the next size up fuse or breaker as long as the calculated load does NOT exceed the ampere rating of the wire.

So yes u could use 4/0 AL on a 200a breaker IF the load calcs come out to 180a or less.

 

[sands35]

I'll do the house load calcs based on what is on the panel. 1st pass says ~90-100 amps.

It's not a heavily loaded panel.

(from memory...)

1 - 40 amp AC
1 - 30 amp AC
1 - 40 amp oven
6-7(?) - 20 amp light / outlets - lightly used.

I need to check all the circuits on that panel.

Thanks for the help!

 

[sberry]

Remember the real run is well less than the breaker rating for the AC.