Question about parallel 200A panels

Status
Not open for further replies.
W

Wattman

Member
Hello I have read over a lot of post on here and it appears you guys like the technical stuff so here is a question, I have about parallel 200A panels

Current Configuration
I have a 460vac 400A panel that contain a main and a 150A breaker feeding a 3-phase 75KVA transformer (460 P -120/208 Sec) indoors which currently feeds ?Panel A? buss rated 250A buss containing a 225A main breaker and 30 spaces, this panel has feed thru lugs and feeds ?Panel B?, which is beside it, also 250A buss and it has no main and 42 spaces.

Question 1
I have to replace Panel A and maybe Panel B in the future, due to the vintage :bye: ? Keeping the existing 75KVA Transformer and the 150A breaker feeding it, I believe I can add a ?New Panel A? Square D NF Series (not QO) with one 250A Main lug 3-phase Panel containing 42 space with ?No Main Breaker? :? the supply conductor will be it 3-3/0 & 1-#4 THHN approx. 20' long. Question is ?Do I have to have a Main Breaker? ?? I believe I can get by with no main breaker because the transformer does not have to have secondary protection if primary protection is 125% primary current??? :happyyes:

Reason :eek:hmy:
There are currently approx. 30 ? ?? and several 1" ridged conduits or more entering the top existing panels A & B ? I plan to add a new 6x6 gutter box above the panel to handle these and allow the circuits to feed into the top of the new panel A via four 2-1/2 nipples ? the 200A feeder will come from the transformer and will enter the bottom of Panel A via an existing lower gutter box. If I select a Panel with a Main Breaker I do not have enough height between the new top gutter box and the existing lower gutter box

Question 2
If the load needs change in the future, can I simply change the transformer from a 75KVA to a 112KVA and breaker feeding it, and add a ?New panel B? 200A Main Lug, No Main Breaker, 42 space, and connect to the transformer with another set of 3-3/0 & 1-#4 THHN approx. 24' long and still be legal??? :lol::thumbsup: :thumbsdown:
 
Last edited:
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Wattman said:
Hello I have read over a lot of post on here and it appears you guys like the technical stuff so here is a question, I have about parallel 200A panels

Current Configuration
I have a 460vac 400A panel that contain a main and a 150A breaker feeding a 3-phase 75KVA transformer (460 P -120/208 Sec) indoors which currently feeds ?Panel A? buss rated 250A buss containing a 225A main breaker and 30 spaces, this panel has feed thru lugs and feeds ?Panel B?, which is beside it, also 250A buss and it has no main and 42 spaces.

Question 1
I have to replace Panel A and maybe Panel B in the future, due to the vintage :bye: ? Keeping the existing 75KVA Transformer and the 150A breaker feeding it, I believe I can add a ?New Panel A? Square D NF Series (not QO) with one 250A Main lug 3-phase Panel containing 42 space with ?No Main Breaker? :? the supply conductor will be it 3-3/0 & 1-#4 THHN approx. 20' long. Question is ?Do I have to have a Main Breaker? ?? I believe I can get by with no main breaker because the transformer does not have to have secondary protection if primary protection is 125% primary current??? :happyyes:

Reason :eek:hmy:
There are currently approx. 30 ? ?? and several 1" ridged conduits or more entering the top existing panels A & B ? I plan to add a new 6x6 gutter box above the panel to handle these and allow the circuits to feed into the top of the new panel A via four 2-1/2 nipples ? the 200A feeder will come from the transformer and will enter the bottom of Panel A via an existing lower gutter box. If I select a Panel with a Main Breaker I do not have enough height between the new top gutter box and the existing lower gutter box

Question 2
If the load needs change in the future, can I simply change the transformer from a 75KVA to a 112KVA and breaker feeding it, and add a ?New panel B? 200A Main Lug, No Main Breaker, 42 space, and connect to the transformer with another set of 3-3/0 & 1-#4 THHN approx. 24' long and still be legal??? :lol::thumbsup: :thumbsdown:
Click to expand...

Maybe......First note that 450 and specifically the chart 450.3(B) you are looking at is concerned with protecting the transformer only. You still need to protect the conductors per article 240, specifically 240.21(C) to see what you have to do. Note that there are only certain circumstances where the primary OCPD can protect the secondary conductors (240.21(C)(1))
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
.....You also must consider protecting the panelboard. 408.36(B). Since you implied it was a delta -wye transformer, the answer would be that you need a OCPD for the panelboard on the secondary side of the transformer..
 
Smart $

Smart $

Esteemed Member
Location
Ohio
electrofelon said:
But there are other ways to protect the secondary conductors. It is possible he could meet the conductor protection without a main breaker, but the panelboard protection definitely puts the brakes on the proposal ( wasn't thinking of the panelboard protection in my first response hence the "maybe").
Click to expand...
That is correct. Under 450 he can opt for primary only protection for the transformer, but there's no way around protection for the panelboard(s). Given that and a wye secondary must have secondary conductor protection, pretty much makes primary only protection a moot issue.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Panelboard protection does not have to be located within the panel being protected, any upstream overcurrent device can provide this protection, if that were not the case there would be little or no purpose of ever using a main lugs only panel.
 
G

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
But could the upstream protection ever be on the line side of an upstream transformer, given that it was properly sized to protect the board?

Sent from my XT1080 using Tapatalk
 
W

Wattman

Member
I appreciate everyone?s input

To me it appears at this point, that I could have Panel A with No main based on 408.36(B) Exception, :D To meet this exception I must comply specifically with 240.21.(C)(1) which appears to debunk the concept in the last sentence. :weeping:

I see it clearly indicates :blink: ?240,21,(C)(1)? specifically! I kind of feel that the (1) should not be there :happysad: , in what cases would I be allowed to use :? (2) or (3) or (4) or (5) you think?

Seams unfair to not be able to use this on a Wye Connection?


OK so I have to have a Main :slaphead: (but at this point only because it?s secondary is specifically a wye connection)

I still need to work out a solution for this project ? So to add a Main I have limited horizontal space as well, that I need to conserve ? I could add a Main quite easily if I went with the QO series but I don?t like the box construction for a industrial project and higher forces require the NF series panels, and it makes sense to keep the site with the same series. So to add a main to Panel A will require me to use a 30 space panel which cause a problem in it?s self and move the lower gutter box down 4 inches, I can do this but still limited due to a 2? wide copper ground buss running under the lower gutter which limits the amount of room. Adding a panel with a main and feed thru lugs is out of the question it is simply to tall.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Smart $ said:
That is correct. Under 450 he can opt for primary only protection for the transformer, but there's no way around protection for the panelboard(s). Given that and a wye secondary must have secondary conductor protection, pretty much makes primary only protection a moot issue.
Click to expand...

But even without the primary OCPD protecting the secondary conductors (when allowed), there are situations where you would not even need a single main breaker at the load end of the secondary conductors to protect the secondary conductors (240.21(C)(2) and (3) (Just talking about secondary conductor protection and Ignoring 408 requirements, just trying to salvage some semblance of credibility from missing them the first time ;) )

Yes, but secondary would have to be 1? 2W or 3? 3W
Click to expand...

...But a delta-wye where NOT using the neutral would not be ok even though it is "3 wire" right?
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Wattman said:
.... QO series but I don?t like the box construction for a industrial project and higher forces require the NF series panels, and it makes sense to keep the site with the same series. So to add a main to Panel A will require me to use a 30 space panel which cause a problem in it?s self and move the lower gutter box down 4 inches, I can do this but still limited due to a 2? wide copper ground buss running under the lower gutter which limits the amount of room. Adding a panel with a main and feed thru lugs is out of the question it is simply to tall.
Click to expand...

Their NQ series, the panelboard version of the QO family, it is now the NQ series, uses the same back box as the NF.

I am sure you will still have height issues, when you use a Main Breaker.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Smart $ said:
Yes, but secondary would have to be 1? 2W or 3? 3W.
Click to expand...
I agree.

jim dungar said:
Their NQ series, the panelboard version of the QO family, it is now the NQ series, uses the same back box as the NF.

I am sure you will still have height issues, when you use a Main Breaker.
Click to expand...
NQ, NF as well as others products use the same series cabinets. Which specific one you need depends on what is installed within. A main breaker kit needs a longer box. Add sub feed lugs, and even more box length is needed. Give up some branch circuit spaces and you can shorten the box.

Wattman said:
I appreciate everyone?s input

To me it appears at this point, that I could have Panel A with No main based on 408.36(B) Exception, :D To meet this exception I must comply specifically with 240.21.(C)(1) which appears to debunk the concept in the last sentence. :weeping:

I see it clearly indicates :blink: ?240,21,(C)(1)? specifically! I kind of feel that the (1) should not be there :happysad: , in what cases would I be allowed to use :? (2) or (3) or (4) or (5) you think?

Seams unfair to not be able to use this on a Wye Connection?
Click to expand...
Cases 2,3,4 and 5 are used all the time. Do you ever install overcurrent protection right at the transformer output terminals? Probably not, but you do generally install it according to 2,3,4 or 5.

Why is primary only protection limited to single phase two wire and three phase delta three wire applications? The answer is fairly simple, especially for the single phase two wire application. Current in and current out are always at same ratio as primary to secondary voltage. Protecting one does protect the other from overcurrent in normal load conditions - a ground fault on the primary however would require the protection be in the primary supply.

Now take a 50 kVA single phase transformer with 120/240 secondary and connect all 50 kVA to just one 120 volt half of the secondary. The primary overcurrent device will see 50 kVA of actual load and will not respond, the loaded half of the secondary however is carrying double the amount it was designed for and will overheat. 50kva @ 240 is about 208 amps, put all 50 kVA on one half @ 120 volts and it draws about 416 amps.

You can say most of the same thing for delta 3 wire only secondary, especially if only serving a three phase load. If you happen to be serving single phase loads there is probably some higher risk of unbalancing enough to overload something, but I think that risk is even higher with a wye secondary. And the transformer primary also has to be delta to use primary only protection.
 
A

arion

Member
Location
sapporo Hokkaido Japan
electrofelon said:
But there are other ways to protect the secondary conductors. It is possible he could meet the conductor protection without a main breaker, but the panelboard protection definitely puts the brakes on the proposal ( wasn't thinking of the panelboard protection in my first response hence the "maybe").
Click to expand...

im still reading my new 2014 nec book.. but i assume if one were to install limiters in the secondary leads that would if chosen carefully act as ocpd on the secondary by limiting the fault ?
 
Smart $

Smart $

Esteemed Member
Location
Ohio
arion said:
im still reading my new 2014 nec book.. but i assume if one were to install limiters in the secondary leads that would if chosen carefully act as ocpd on the secondary by limiting the fault ?
Click to expand...
Carefully chosen, perhaps... from a purely technical perspective. However, the NEC does not recognize limiters as ocpd.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Smart $ said:
Carefully chosen, perhaps... from a purely technical perspective. However, the NEC does not recognize limiters as ocpd.
Click to expand...

The real question I think, is if NEC would recognize cable limiters as a method of reducing available fault current, or if they even will reduce fault current?
 
Status
Not open for further replies.
Top