Sizing lightly-loaded high-leg service conductor

[LarryFine]

I have a thought
generally in commercial the meter box has test and by pass
Why not use 1 sigle phase pane feed from the meter and a 3 phase 30 amp switch fed from the meter also. You can get stacking lugs if side by side will not fit.
Just an Idea

Hmmmmmm. :roll: I shall reconsider.

 

[LarryFine]

My initial thought (the post I deleted, which then got removed entirely) was to use a multi-disconnect meter pan combo and split off 1? and 3? feeders...

I would rather have a separate single phase panel and three phase disconnect than a three phase panel with one bus essentially unused.

I would prefer to have a separate single phase and 3 phase panel, especially with the 208V to neutral running around a high leg service.

IMHO best value would be having a small 3 phase panel or single 3 phase disconnect, and a 200A single phase panel, with the B leg conductor sized for the small panel, and A, C, and N sized for the service as a whole.

Why not use 1 single phase panel fed from the meter and a 3 phase 30 amp switch fed from the same meter also. You can get stacking lugs if side by side will not fit.

Upon reflection (and pricing), I have come to agree with you guys. I would like to use a 3ph panel for the 3ph load, and a 1ph panel for everything else. Of course, this leads to several new questions:

1a) I have sized the service conductors at #3/0 for the main panel's 200a breaker. If I add another service panel, such as a 12-space main-lug, to contain the 3-pole breaker, I now have 230a worth of main breaker.

1b) Starting at the meter, the minimum allowed in a meter larger than 100a is #4. Being a 200a meter, would I be allowed to supply a 200a panel as well as a second, smaller one, or do I need to step up to a 320a meter base?

1c) Must the line-side-of-the-meter #3/0 now be upsized, say to #4/0, even though it will be carrying the same calculated load?

2) I take it that, for the load-side of the meter, the high-leg conductor should match that of the line side, as well as the other two lines. I can fit three #4's and a #10 in a 1" EMT, I think.

3a) This means I need a high-leg lugs to fit #4, as well as two double lugs, each one to receive one #3/0cu and one #4cu. Anyone know of double lugs with different-sized holes. or a range that covers both sizes?

3b) Sierra mentioned stacking lugs, which I take to mean taller, but not wider, than a single lug. This would be good, since the studs are fairly close, and the high-leg must connect to the meter's C-phase.

From Dominion Power's Blue Book:

 

[LarryFine]

Oh, one more thing: without a single main breaker in the smaller panel, how are the conductors protected at not more than their ampacity?

Thanx, all!

 

[winnie]

For question 1), see 230.90(A), in particular exception 3.

-Jon

 

[Smart $]

Oh, one more thing: without a single main breaker in the smaller panel, how are the conductors protected at not more than their ampacity?

Thanx, all!

You started losing me at question "1a" :grin:

You cannot have a 1? service disconnect and a 3? MLO panel. Any way you go about it, a 3? service disconnect is required.

 

[Smart $]

Oh, one more thing...

Sorry about my last post... pulled an all-nighter and my thinking was quite a bit fuzzy when I made it.

I suppose what you are proposing is OK, but highly irregular as such IMO.

Is there a reason why you would not run three #3/0 and a #4 (for the high-leg) to an MLO service panel, slap in one 30A 3P and one 200A 2P CBs, and feed an MLO 1? panel off the 200. I believe this is quite similar to what you had in mind, but groups the service disconnects.

 

[LarryFine]

You cannot have a 1? service disconnect and a 3? MLO panel. Any way you go about it, a 3? service disconnect is required.

Is there a reason why you would not run three #3/0 and a #4 (for the high-leg) to an MLO service panel, slap in one 30A 3P and one 200A 2P CBs, and feed an MLO 1? panel off the 200. I believe this is quite similar to what you had in mind, but groups the service disconnects.

Just to clarify, my intent is to use a 1ph 200a main-breeaker panel and a 3ph 125a main-lug panel. These will be back-to-back with the 200a 3ph meter, which can be upped to 32a if necessary.

Counter-question: If I place the 3ph 12-sp panel net to the 1ph 200a panel, wouldn't the 200a main breaker and the few (only one right now; the A/C) breakers in the 3ph panel qualify as grouped?

The pre-existing old service had a large J-box with split-bolts fed from the meter load-side terminals. The A/C branch circuit was fed from these split-bolts by three #10's into a 3-pole fused switch.

Also fed from the split-bolts (except from the hi-leg, of course) was the 100a 1ph panel for lights, the air-handler/gas furnace, and a couple of receptacles. The entire existing service is being razed.

I've already canceled the order for the 3ph 200a panel, and will use a 1ph 200a panel. What is up for debate is whether to use a new 12-sp main-lug panel, or even re-use the existing fused switch.

Is there any reason the 6-throws-of-the-hand disconnect rule would not apply to the 200a 1ph main breaker and no more than the A/C's 3ph 30a breaker, and any four additional breakers, in the adjacent 3ph panel?

 

[Smart $]

Just to clarify, my intent is to use a 1ph 200a main-breeaker panel and a 3ph 125a main-lug panel. These will be back-to-back with the 200a 3ph meter, which can be upped to [320a] if necessary.

I understood your intent.

Counter-question: If I place the 3ph 12-sp panel net to the 1ph 200a panel, wouldn't the 200a main breaker and the few (only one right now; the A/C) breakers in the 3ph panel qualify as grouped?

I believe they would [read: my opinion doesn't count :grin: ] provided each of these breakers is permanently marked as service disconnects.

The pre-existing old service had a large J-box with split-bolts fed from the meter load-side terminals. The A/C branch circuit was fed from these split-bolts by three #10's into a 3-pole fused switch.

Also fed from the split-bolts (except from the hi-leg, of course) was the 100a 1ph panel for lights, the air-handler/gas furnace, and a couple of receptacles. The entire existing service is being razed.

Service entrance conductors are permitted to be tapped and each tap conductor must terminate at a service disconnect.

I've already canceled the order for the 3ph 200a panel, and will use a 1ph 200a panel. What is up for debate is whether to use a new 12-sp main-lug panel, or even re-use the existing fused switch.

The deciding factor here is the likelihood of added 3? loads in the future.

Is there any reason the 6-throws-of-the-hand disconnect rule would not apply to the 200a 1ph main breaker and no more than the A/C's 3ph 30a breaker, and any four additional breakers, in the adjacent 3ph panel?

None that I can think of.

Is there that much difference in cost to have the 200A 1? main breaker in the 1? panel? It would make a much neater install having the 200A 1? main in the 3? service panel. However, I understand that in a 12 space panel, the 200A 2P breaker would have to be positioned on spaces 5,7 or 6,8 if B leg is your hi-leg... thereby limiting total 3? breakers to two on the opposite side.

 

[LarryFine]

So far, so good. Next (already asked but not answered) question: Will I now need a 320a meter, since (A) I will have greater than 200a worth of disconnect OCP, and (B) the 200a meter base is not rated for more than one set of load conductors.

I'm basing statement B on the fact that the 320a meter base states suitable for more than one set, while the 200a meter does not. To wit: "405.3 Two separate panels may be served from this meter base." The 200a base does not have this sentence.

If I can stick with the 200a meter base, since the total demand is still well within the rating, I'll have to tap two of the #4's that will feed the 125a panel from the 3/0's feeding the 200a panel. I was hoping to avoid needing a trough, but if I gotta, I gotta.

I just had another thought: Will I need to upsize the conductors ahead of the meter, as well as the untapped portion after the meter, since there will be greater than 200a of OCP supplied by them? I have 3/0 cu in the design, but will I have to go up to 4/0 cu?

 

[Smart $]

So far, so good. Next (already asked but not answered) question: Will I now need a 320a meter, since (A) I will have greater than 200a worth of disconnect OCP, and (B) the 200a meter base is not rated for more than one set of load conductors.

I'm basing statement B on the fact that the 320a meter base states suitable for more than one set, while the 200a meter does not. To wit: "405.3 Two separate panels may be served from this meter base." The 200a base does not have this sentence.[/

I'm not knowledgeable enough on service requirements to answer this question without checking and double checking the "book". I don't mean to keep you hanging but I currently have other obligations that need attending. Perhaps someone else can provide the answer before I can get back to you...

If I can stick with the 200a meter base, since the total demand is still well within the rating, I'll have to tap two of the #4's that will feed the 125a panel from the 3/0's feeding the 200a panel. I was hoping to avoid needing a trough, but if I gotta, I gotta.

This is why I have been trying to convince you to use a 3? service panel. No taps required.

I just had another thought: Will I need to upsize the conductors ahead of the meter, as well as the untapped portion after the meter, since there will be greater than 200a of OCP supplied by them? I have 3/0 cu in the design, but will I have to go up to 4/0 cu?

Most likely... but this is another "I'll have to get back to you later".

 

[winnie]

I answer in concert with Smart$: I don't know enough to simply say 'this is so', however 230.90(A) exception 3 seems pretty clear to me.

The total of the OCPD ratings fed by the service conductors can exceed the ampacity of the service conductors, as long as the total calculated load is less than the ampacity of the service conductors. I believe that there would be no problem with using a 200A single phase breaker and a 30A three phase breaker as your combined service disconnect, along with 200A service conductors and a 200A meter.

You do bring up a good point that it may be more _convenient_ to use a 320A meter base, simply because it is common practise to feed two panels in this situation, and thus the lugs are designed to feed two panels. It also may be _cheaper_ to do this then to provide the appropriate splicing.

Gosh this situation is exactly what 'delta' breakers were made for. Too bad they are explicitly prohibited *grin*.

-Jon

 

[Smart $]

Well I've checked and double shecked "the book" from every angle I could conceive and your good to go with the 200A meter scenario as stated... except for one issue... and that is, I found no requirement that says you have to install an auxiliary gutter ("trough") for the taps... so if you can manage, you can do so in either of the panels.