wrong?

[hardworkingstiff]

It is very common around here to run a #4-4c type W cable to a pedestal for shore power for boats and installing it on a 100-amp breaker (usually feeding two 50-amp receptacles). Table 400.5(B) 75c column E (because only 2 conductors are current carrying) gives and ampacity of 115-amps.

Engineers have drawn it this way, plan review has approved it, inspectors have passed it, many times.

I believe this to be wrong (as of a few minutes ago). Anyone care to comment please?

Edit: I think I just found the reason it's been OK, sorry all.

 

[augie47]

we're not going to let you off that easy
Do the receptacles have OCP ?

 

[hardworkingstiff]

we're not going to let you off that easy
Do the receptacles have OCP ?

Yes, the power centers have 50-amp breakers in them feeding the receptacles. The W cable (feeder to the power center) hits a buss bar in the power center and then the taps off the buss bar to go to the breaker and the breaker feeds the receptacle.

I was thinking that 110.14 (C)(1) might prohibit us from using the 115-amp 75c ampacity in table 400.5(B), but as I digested it more, the power center buss bar is rated for 75c connections.

What got me going was this note in step 3 of 400.5 in the 08 handbook

It should be noted that compliance with 110.14(C) is based on Table 310.16 conductor ampacities, and the ampacity from that table for a 75c, 3/0 AWG copper conductor is 200 amperes. Therefore, this cable with 3/0 conductors operating at 200 amperes (noncontinuouse plus continuous loads, is of sufficient physical size to dissipate the heat occuring at the equipment terminations.

Actually, now that I read it again, the handbook seems to indicate that we are bound by 310.16 ampacities when using W cable because of 110.14(C). If this is so, I know of a BUNCH of marinas that are not in compliance.

 

[augie47]

I may be missing something,. but I don't see a problem. 110.14 directs to use 75? conductor rating, 555.13 allows us to use type W and you are within the 75? rating.
The handbook commentary is for guidance only and they probably didn't take this somewhat unusual setup into consideration.

 

[hardworkingstiff]

I may be missing something,. but I don't see a problem. 110.14 directs to use 75? conductor rating, 555.13 allows us to use type W and you are within the 75? rating.
The handbook commentary is for guidance only and they probably didn't take this somewhat unusual setup into consideration.

If you have the 08 handbook, look at the application example in column 2 of page 482. It specifically mentions 555.13 and in step 3 I get the BAM in your face comment that is just killing me.

 

[augie47]

My '08 Handbook isn't available at the moment. I will check it tomorrow.
By then someone else may solve the dilemma.

 

[hardworkingstiff]

info so far

info so far

I spoke with engineers, and electricians today about this and this is what I understand so far.

If you terminate the #4 type W cable on a 75C breaker, then 85-amps is the ampacity per 110.14(C)(1) which says I must use the 75C column of table 310.16 instead of 115-amps of the 75C column for 2 CCCs of table 400.5(B).

I can butt splice (T&B says theirs is rated 150C and the heat shrink is rated for 90C) the #4 type W conductor to a #3 code wire conductor in the panel and the termination will be good for 100-amps (75C for #3 in table 310.16). Nothing says how long the #3 has to be.

NFPA called back and "off the record" said they thought there was a lug/terminal that could be used at the breaker that would act like a heat sink that would allow the termination of the W cable and have the 115-amp rating. I'm not sure what they were talking about, but think maybe it's a pin terminal but I did not get to talk to a manufacturer about this.

I'm pretty sure the bus bar with 3/8" threaded studs in the power center is rated for a 90C termination (T&B ring terminals I use are rated 150C), so 310.16 90C for #4 gives me a 95-amp rating (instead of the 115-amp 75C rating of the W cable with 2 CCCs).

WHEW!