Over head line

[chadwiseman]

I have a section of 4160 overhead line that is 336ACSR and then drops down to 2/0 ACSR. According to the code I'm suppose to set my upstream breaker to protect the 2/0 ACSR. However this will cause nuisance trips as the heavier 336 ACSR has heavy loads. I've been told that the other option is to use a recloser at the 2/0, since fuses are not advisable for systems supplying motor loads. However the motor loads are at 600 V after a step down transformer. Is there any way around using the recloser?

 

[davidbeach]

Code?, What Code? If you are referring to the NEC, look at 240.21(B)(5) and see if applies to your situation. You may be able to protect the 336 and consider the 2/0 a tap with the its protection at its end rather than at its source.

 

[chadwiseman]

The problem is that the 2/0 has multiple small taps along its length. However, I am referring to the NEC.

 

[cuky2000]

If this work is performed by a utility, the compliance with the NEC is optional. Probably the utility standard may provide a guideline in this case.

If this work is in commercial or industrial environment performed by a contractor or consulting firm, it is require to comply with the NEC.

Check if the enclose information could be applicable in your system.

http://127.0.0.1:4664/redir?url=C:\...chema=8&start=1&s=ITUxP6wfA29sdCYTVR3vUzb_mxg

 

[chadwiseman]

This is an industrial setting. Fuses would be cheap, but some people are afraid of losing a phase and damaging machines, so they want reclosers (which are expensive). Has anyone had experience with overhead fuses supplying large motor loads like this?

 

[davidbeach]

cuky2000, your link is directed to a file saved on your system. 127.0.0.1 is the loop back address.

 

[cuky2000]

Here are the links:

http://www.bussmann.co.uk/images/Complete cats/High Voltage/ASL.pdf

http://www.sandc.com/edocs_pdfs/EDOC_001687.pdf

 

[jghrist]

The code allows breaker relay settings of as much as three times the ampacity of the conductor (Art. 240.101 in NEC-2002). The ampacity of 2/0 AAC is 255A in Table 310.21 and ACSR would have a higher ampacity. The relay pickup could be up to 765A.

Most utilities use fuses on overhead taps without regard to whether or not customers have 3Ø motor load, and depend on the customers having single-phasing protection for their motors. Many utilities would, however, use 3Ø protective devices for circuits that serve mostly industrial loads.

You could also consider sectionalizers on the taps as a less expensive alternative to reclosers.

 

[davidbeach]

jghrist, actually the code section cited permits a breaker to be set at 6 times ampacity, fuses are limited to 3 times ampacity. The difference is because medium voltage fuses operate at twice their amp rating. The end result is that the NEC requirement for protection of medium voltage conductors is strictly short circuit protection, no overload protection.

 

[PowerfulStuff]

86ranger,
Have you considered putting phase loss protection in as part of the motor control? Depending on your circumstances, this may be a lot cheaper.

Regards,
PowerfulStuff

 

[chadwiseman]

Is anyone aware of the Canadian Electrial Requirement for protecting 2/0 ACSR. I was under the impression that we had to protect it to its ampacity (255A). However, as we are in a northern climate we use a multiplying factor to increase this slightly. However, from what others are saying about the NEC, it may be possible to set the overcurrent protection above the ampacity of the cable. Anyone have any insight?