Feed Through On MDP

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WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
Question for you all.
We have specified a 2500A main service disconnect to protect our 2500A MDP.
MDP has 2 breakers (2000A & 600A) Serving SDP1 (2000A) and SDP2 (600A).
SDP2 is 200' away from MDP and does not currently have an MCB.

Electrician is proposing on tapping SDP2 feeder straight off MDP bus in a feed through fashion, and installing an enclosed 600A circuit breaker near SDP2 gear as its "MCB" OCPD.
Is this code compliant? If not, please post an article or reference. Technically its protected at its source through 2500A service disconnect, and 600A ECB.
Hypothetically if 600A lugs will even allow the tap on 2500A bus, what issues may result aside from potential increase in Fault current?

Thanks in advance.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
If I'm reading this correctly you want to tap the 2500 amp bus and run tap conductors 200' to the enclosed circuit breaker near SDP2? Unless those tap conductors are run completely outside of the building you would need to comply with the 25' tap rule, 200' is too far.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I'm confused. The OP states he has a 2500 and a 600 amp breaker in the MDP. Why does he need an OCPD at the distant panel?
2500 amp main breaker as the service disconnect and then two feeder breakers in the MDP, 2000 and 600 amp.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I meant to say a 2000 (not 2500) and a 600 in a MDP with a 2500 amp main. So why does he need another breaker at the distant 600 amp panel?
Good question, maybe so that they will have the 600 amp for another load or to keep it as a spare?
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
If I'm reading this correctly you want to tap the 2500 amp bus and run tap conductors 200' to the enclosed circuit breaker near SDP2? Unless those tap conductors are run completely outside of the building you would need to comply with the 25' tap rule, 200' is too far.
Conductors wont be ran to the building exterior, as the shortest path (by 75'or so) is through the interior. "I" am not wanting to, EC is suggesting alternatives to my design.

So technically, per tap rule, (rather than using 600A breaker inside MDP enclosure) EC can tap off MDP buss to feed 600A ECB (serving SDP2), if and only if, ECB is within 10' of MDP.

I've never used ECB in this way before. Usually I've only used ECB as equipment local disconnect or coordination purposes for MLO panels.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Conductors wont be ran to the building exterior, as the shortest path (by 75'or so) is through the interior. "I" am not wanting to, EC is suggesting alternatives to my design.

So technically, per tap rule, (rather than using 600A breaker inside MDP enclosure) EC can tap off MDP buss to feed 600A ECB (serving SDP2), if and only if, ECB is within 10' of MDP.

I've never used ECB in this way before. Usually I've only used ECB as equipment local disconnect or coordination purposes for MLO panels.
If the conductors are 1/3 or larger than 2500 amps then you can use the 25' tap rule otherwise you're correct you're stuck with the 10' tap rule.
 

jap

Senior Member
Occupation
Electrician
Question for you all.
We have specified a 2500A main service disconnect to protect our 2500A MDP.
MDP has 2 breakers (2000A & 600A) Serving SDP1 (2000A) and SDP2 (600A).
SDP2 is 200' away from MDP and does not currently have an MCB.

Electrician is proposing on tapping SDP2 feeder straight off MDP bus in a feed through fashion, and installing an enclosed 600A circuit breaker near SDP2 gear as its "MCB" OCPD.
Is this code compliant? If not, please post an article or reference. Technically its protected at its source through 2500A service disconnect, and 600A ECB.
Hypothetically if 600A lugs will even allow the tap on 2500A bus, what issues may result aside from potential increase in Fault current?

Thanks in advance.

This doesn't complete sense to me yet.

Why would your design not incorporate the 600a feeder breaker into Panel SDP1 and make Panel SDP1 a 2500 amp piece of gear?
Why have a 2500 amp service disconnect feed a Panel MDP with only 2 breakers in it?

You say your 2500 amp MDP already has a 600 amp breaker in it to feed panel SDP2.
Regardless of how far Panel SDP2 is from Panel MDP, if it's inside the same building, It doesn't require a Main Circuit breaker "At" Panel SDP2.
The "Feeder" to panel SDP2 is already protected by the 600a breaker in Panel MDP.

My question is, Is the 600a Panel SDP2 "existing"? or are you adding a new 600a Panel SDP2 to the building and need somewhere to feed it from?

Why would the electrician even bring up tapping the 2000 amp buss and setting a 600a ECB if there was an existing 600a breaker to begin with?

To me, it sounds like you have an existing 2000 amp feeder an existing Panel SDP1, but, nowhere to originate an additianal 600a Feeder.

Is that the case? or am I all wet?

JAP>
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
This doesn't complete sense to me yet.

Why would your design not incorporate the 600a feeder breaker into Panel SDP1 and make Panel SDP1 a 2500 amp piece of gear?
Why have a 2500 amp service disconnect feed a Panel MDP with only 2 breakers in it?

You say your 2500 amp MDP already has a 600 amp breaker in it to feed panel SDP2.
Regardless of how far Panel SDP2 is from Panel MDP, if it's inside the same building, It doesn't require a Main Circuit breaker "At" Panel SDP2.
The "Feeder" to panel SDP2 is already protected by the 600a breaker in Panel MDP.

My question is, Is the 600a Panel SDP2 "existing"? or are you adding a new 600a Panel SDP2 to the building and need somewhere to feed it from?

Why would the electrician even bring up tapping the 2000 amp buss and setting a 600a ECB if there was an existing 600a breaker to begin with?

To me, it sounds like you have an existing 2000 amp feeder an existing Panel SDP1, but, nowhere to originate an additianal 600a Feeder.

Is that the case? or am I all wet?

JAP>
All new construction from top to bottom. Nothing is existing.

Correct "Regardless of how far Panel SDP2 is from Panel MDP, if it's inside the same building, It doesn't require a Main Circuit breaker "At" Panel SDP2.
The "Feeder" to panel SDP2 is already protected by the 600a breaker in Panel MDP."

"My question is, Is the 600a Panel SDP2 "existing"? or are you adding a new 600a Panel SDP2 to the building and need somewhere to feed it from?" The building is a split service. One tenant (hotel) is using the 2000A portion, a large restaurant is using the 600A portion. Our drawings indicate SDP2 is protected at MDP (technically service disconnect). EC turned in submittals for approval of ECB method.

"Why would the electrician even bring up tapping the 2000 amp buss and setting a 600a ECB if there was an existing 600a breaker to begin with?" I agree which is why I started the post.
 

jap

Senior Member
Occupation
Electrician
I'm just trying to figure out the need for a 2500a Service Disconnect Structure (with evidently overcurrent protection) feeding a Panel MDP structure with only 2 breakers in it, then, feeding a Panel SDP1 and Panel SDP2 from Panel MDP.

(4) Structures?

Why not incorporate all the breakers in Panel SDP1 and the 600 amp feeder breaker all into 1 2500 amp Panel and call it Panel MDP fed from the 2500 amp Service Disconnect and drop down to (3) total structures?

Oh well.

Jap>
 

WA_Sparky

Electrical Engineer
Location
Vancouver, WA, Clark
Occupation
Electrical Engineer
I'm just trying to figure out the need for a 2500a Service Disconnect Structure (with evidently overcurrent protection) feeding a Panel MDP structure with only 2 breakers in it, then, feeding a Panel SDP1 and Panel SDP2 from Panel MDP.

(4) Structures?

Why not incorporate all the breakers in Panel SDP1 and the 600 amp feeder breaker all into 1 2500 amp Panel and call it Panel MDP fed from the 2500 amp Service Disconnect and drop down to (3) total structures?

Oh well.

Jap>

I should have just posted a picture in the OP to clear up confusion. I hope this explains it better. Technically I didn't need the 2500A Breaker, it could have been a fused switch instead.

MSD = MDP reference in original post.
MDP2 = SDP2 reference in original post.
2000A breaker shown = "SDP1" reference in original post.

Background: SDP1 was permitted a couple months before this project, so technically SDP1 is existing but not constructed yet.

Just curious if anyone catches any design flaws I could keep in mind for future projects. I'm more familiar with the engineering side of things rather than cost or constructability aspects design.

"Why not incorporate all the breakers in Panel SDP1 and the 600 amp feeder breaker all into 1 2500 amp Panel and call it Panel MDP fed from the 2500 amp Service Disconnect and drop down to (3) total structures?"
Yes agreed and that's what I have designed. (3) total structures; (1) Service disconnect, and (2) metered distributions.

My approach was to have service disconnect on building exterior containing (2) breakers, (1) hotel and (1) restaurant, therefore only two metered services paid for.

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