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j.orlett

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A 1600 amp,480 volt service. The service has 4 each 4 e.m.t.s with 900AL wire into the M.d.p. There is a 3/0 copper through a lug on the building steel, continuos to the copper water service. There is a #6 copper to a ground rod. There is a #1/0 copper looped to the 4 each bonding bushings and all grounds and neutrals connected together. Does the 1/0 on the bushings legal in size?
 
I agree with Justin. The service raceway must be bonded with a conductor sized according to 250.66. A simple solution would be to install bonding wedges between the locknut and the metal can. That's if no concentric, eccentric or tangential KO's are used.
 
What is the largest size service entrance conductor ?.. If 900AL. than 1/0 copper is fine.
 
if these are parallel sets than the bonding jumper needs to be not less than 12.5 % of the total area of the largest set
 
M. D. said:
if these are parallel sets than the bonding jumper needs to be not less than 12.5 % of the total area of the largest set
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That only applies to phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, and the size has to be adjusted if the bonding jumper(s) is(are) of a different material than the phase conductors.
 
NEC diegest

The sizing requirements for the main bonding and system bonding jumpers are covered in 250.28(D). Where there are parallel sets of service or supply conductors and the total circular mil area for the largest individual phase set exceeds 1100 kcmil copper or 1750 kcmil aluminum (the point at which Table 250.66 reaches it maximum size), the MBJ or SBJ is sized based on 12.5% of the largest parallel set. This section also covers the method for sizing the MBJ or SBJ where the bonding jumper conductor material differs from that of the circuit conductors. The following is an example of sizing a copper main or system bonding jumper where the ungrounded conductors are installed in parallel:

4 sets of parallel 500 kcmil (500,000 cmil) copper supply conductors.

All parallel sets (A, B, & C phases) are the same size.

Largest individual phase set: 4 x 500,000 = 2,000,000 cmil.

MBJ or SBJ size: 2,000,000 x .125 (12.5%) = 250,000 cmil

MBJ or SBJ = 250 kcmil copper

Another example using aluminum ungrounded conductors were aluminum and a copper bonding jumper.

2 sets of parallel 750 kcmil (750,000 cmil) aluminum supply conductors

All parallel sets (A, B, & C phases) are the same size.

Largest individual phase set: 3 x 750,000 = 2,250,000 cmil.

MBJ or SBJ size:
 
MD is correct. Once you've passed the 1100 or 1750 kcmil threshold of 250.66 you need to go the the 12.5% formula. The supply side equipment bonding jumper is sized according to 250.28(D) as MD stated.
 
infinity said:
MD is correct. Once you've passed the 1100 or 1750 kcmil threshold of 250.66 you need to go the the 12.5% formula. The supply side equipment bonding jumper is sized according to 250.28(D) as MD stated.
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I'm not contesting MD's statements for MBJ and SBJ. However the OP question is regarding the 1/0 copper run serially to the grounding bushings. The way the OP is worded I interpreted the 1/0 copper to be an Equipment Bonding Jumper on Supply Side of Service falling under 250.102(C). The wording of 250.102(C) is initially the same as 250.28(D), but the two additional sentences change the sizing parameters.
 
Smart $ said:
I'm not contesting MD's statements for MBJ and SBJ. However the OP question is regarding the 1/0 copper run serially to the grounding bushings. The way the OP is worded I interpreted the 1/0 copper to be an Equipment Bonding Jumper on Supply Side of Service falling under 250.102(C). The wording of 250.102(C) is initially the same as 250.28(D), but the two additional sentences change the sizing parameters.
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So are you saying that the #1/0 looped from bushing to bushing, used to bond the service raceways, is sized correctly?
 
infinity said:
So are you saying that the #1/0 looped from bushing to bushing, used to bond the service raceways, is sized correctly?
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No, I'm not saying it is sized correctly. I'm just saying it is not sized by combining the size of the same-phase paralleled conductors. Instead it is sized based on largest phase conductor in each raceway, and respective to each raceway.

I'm of the impression 1/0 copper is fine. However, I believe the installation to be in violation because it uses only a single 1/0 copper for all the paralleled raceways, when it should use one for each raceway.
 
Smart $ said:
No, I'm not saying it is sized correctly. I'm just saying it is not sized by combining the size of the same-phase paralleled conductors. Instead it is sized based on largest phase conductor in each raceway, and respective to each raceway.

I'm of the impression 1/0 copper is fine. However, I believe the installation to be in violation because it uses only a single 1/0 copper for all the paralleled raceways, when it should use one for each raceway.
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Thanks for the clarification, I agree. If a single jumper were used for each conduit it would be sized according to the conductors within that conduit. If one conductor were used and looped through all of the bonding bushings than it would be sized based on 12.5% of the total area of the parallel conductors.
 
In order to size the jumper we need to know how many and what size ungrounded conductors are in the 4" emts if they are all the same size and right now it looks as if there are four for each phase. It is the size of the largest ungrounded conductor and in this case it looks as if it is
(4 x 900) = 3600 x .125 = 450

That's the way I read it any way
 
M. D. said:
In order to size the jumper we need to know how many and what size ungrounded conductors are in the 4" emts if they are all the same size and right now it looks as if there are four for each phase. It is the size of the largest ungrounded conductor and in this case it looks as if it is
(4 x 900) = 3600 x .125 = 450

That's the way I read it any way
Click to expand...
450kcmil, if using one continuous aluminum jumper.

If one continuous copper jumper...

(4 x 700 kcmil copper in lieu of 900 kcmil aluminum) = 2,800 kcmil copper, ...x .125 = 350 kcmil copper. You could technically interpolate the equivalent copper size but 600 is definitely too small and the result using 600 would be 300kcmil copper, so you'd have to go up one trade size anyway.

If using the type of grounding bushing that includes the lug, I don't believe the lug is sized big enough to accept copper 350's!
 
Smart $ said:
450kcmil, if using one continuous aluminum jumper.

If one continuous copper jumper...

(4 x 700 kcmil copper in lieu of 900 kcmil aluminum) = 2,800 kcmil copper, ...x .125 = 350 kcmil copper. You could technically interpolate the equivalent copper size but 600 is definitely too small and the result using 600 would be 300kcmil copper, so you'd have to go up one trade size anyway.

If using the type of grounding bushing that includes the lug, I don't believe the lug is sized big enough to accept copper 350's!
Click to expand...


One really good reason to use separate smaller conductors from each bushing.
 
How many of these 900 are in paralell in pipe #1 to make phase A of this 1600 amp service .Given the information isn't that the largest conductor in the pipe??
 
electricain

electricain

Thanks for all the replys. There is 4 each #900 al. IN each of the 4, 4 inch e.m.t.s. I was Intending to run a jumper to each e.m.t.. 3 HOTS/ 1 NEUTRAL.
 
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