Replacing Motor therminal box (peckerhead)

[gilly]

I have a problem with a peckerhead and was wondering if anyone out there has come acrossed this, and if you have any suggestions

I have a 400hp motor that will be feed with Parallel 4" conduits the peckerhead has only 1 - 4" opening. I thought about setting a pull box and running my 2 conduits to it then bringing one 4" to the peckerhead but then I get into derating becuase the length of flex will not be that short with 4" (by the way the conductors are 350's VFD cable that is why the conduit is so large)

The other problem is that the motor has 4 conductors per phase along with my 2 conductors per phase is a lot of wire in the peckerhead. The factory peckerhead is 15.2"L x 10.2"W x 8.8"D not enough room for the terminations.

What I would like to do is have my fab shop beef up the back of a hoffman type 24x24x12 Nema 4x j-box, (motor is outside) and cut the mounting patteren into the back of that. Then I could use the factor gasket and mount the box directly to the motor, then I would have room to make the terminations.

I have talked to the motor manufactur to see what they suggest but the first person I talked to did not have a problem with my box idea he wanted to run it by the applications eng first.

What are your thoughts.

 

[petersonra]

It seems like a perfectly reasonable solution to me, so my guess is that it is somehow prohibited.

If it was me, I might just add the larger box next to the peckerhead (love the word BTW), and run the motor leads into the other box for termination.

 

[rbalex]

Oddly enough, it would more likely violate the Hoffman box listing rather than the motor's (which doesn't have one). However, there are certain Code requirements for motor terminal boxes that you would have to keep in mind – see Section 430.12 for example. Since you have already contacted the manufacturer, I'm surprised they didn't suggest that they could provide a larger motor terminal box.

 

[nollij]

I'm surprised they didn't suggest that they could provide a larger motor terminal box.

Personally, I would contact the motor manufacturer and ask if they can provide a larger peckerhead and 2 - 4" openings. A state inspector where I am located would almost assuredly not accept that sort of modification to a Junction Box.

 

[gilly]

I just received an email from Toshiba and this was the response

Customers and end users often replace with the Hoffman type box.
Toshiba has no issue with this.

So should I go with it.

 

[petersonra]

Since it is VFD cable, why do you need to run it in flex at all?

 

[steve66]

I just received an email from Toshiba and this was the response

Customers and end users often replace with the Hoffman type box.
Toshiba has no issue with this.

So should I go with it.

I know this doesn't help, but it sounds to me like their engineer just admited they make their boxes too small.

 

[rbalex]

From the information you have provided, I?m assuming the motor is 460V and the VFD output rating is 477A or maybe a bit larger. In any case, it appears to me that Toshiba owes you a larger motor terminal box. See the last line of the second section in NEC Table 430.12(B). The dimensions you mentioned would result in a cubic volume of 1364 cu-in. The table indicates you should have a minimum of 1540 cu-in. [Read the Table in context of Section 430.12(B)] NEMA MG-1, Table 4.6 indicates a minimum usable volume of 2000 cu-in for your motor.

The Hoffman box you mentioned would be GINORMUS;it would certainly give you plenty of room, but you still would need to review all the other requirements of 430.12, especially 430.12(E).

 

[Cow]

We've replaced motor j-boxes in the past like you've described. We haven't had an issue yet but I've never brought it to the inspectors attention either. Usually it's because the factory box is either damaged or missing.

 

[weressl]

From the information you have provided, I?m assuming the motor is 460V and the VFD output rating is 477A or maybe a bit larger. In any case, it appears to me that Toshiba owes you a larger motor terminal box. See the last line of the second section in NEC Table 430.12(B). The dimensions you mentioned would result in a cubic volume of 1364 cu-in. The table indicates you should have a minimum of 1540 cu-in. [Read the Table in context of Section 430.12(B)] NEMA MG-1, Table 4.6 indicates a minimum usable volume of 2000 cu-in for your motor.

The Hoffman box you mentioned would be GINORMUS;it would certainly give you plenty of room, but you still would need to review all the other requirements of 430.12, especially 430.12(E).

..if I might add: if I would choose to go with the non-factory box I would add a terminal block to properly terminate the 6 conductors per phase.

Bob, I like your technical description: GINORMOUS

 

[George Stolz]

Bob, I like your technical description: GINORMOUS

I think I saw that in the Index somewhere.

 

[gilly]

Thanks for all the help