Paralleling fuses.

[aelectricalman]

The utility company we are working with will not work on a customers primary line if it is fused over 200amp Primary because they do not stock fuses large enough to service the equipment. We have a customer that has a need of 400 amps Primary capacity. Assuming all wire sizing is ample, what are the disadvantages of installing (2) sets of 200amp fuses in parallel per phase?

 

[roger]

If this is under the NEC it will be in violation of 240.8

240.8 Fuses or Circuit Breakers in Parallel.
Fuses and circuit breakers shall be permitted to be connected in parallel where they are factory assembled in parallel and listed as a unit. Individual fuses, circuit breakers, or combinations thereof shall not otherwise be connected in parallel.

Roger

 

[jim dungar]

Why doesn't the customer purchase and maintain control over their own spare fuses?
Why are you putting in 400A circuits when the utility can only provide 200A?
What voltage are you at?

Part of the issue of paralleling fuses is the current distribution as only one of the devices is opened either during fault interupption or during routine switching.

 

[aelectricalman]

Why doesn't the customer purchase and maintain control over their own spare fuses?
Why are you putting in 400A circuits when the utility can only provide 200A?
What voltage are you at?

Part of the issue of paralleling fuses is the current distribution as only one of the devices is opened either during fault interupption or during routine switching.

Its cheaper to let the utility manage it. They are the areas largest customer. The utility services them for free. They would have to hire it out.
The utility can provide 400amp Knived switched or 600 switches but they dont have overcurrent protection. The only purpose of these fuses is to protect the Utility. The customer has other overcurrent protection on down the line. Its a customer owned system too.

12.47kV

 

[aelectricalman]

I was thinking about using 1 set of (2) 200 amp cutouts per phase.

If you think its not code compliant, is there an option where there is a multiple socket cut out, or did I miss the point.

 

[jim dungar]

I meant for the customer to buy the 400A fuses, and let the utility do the actual work. We have done this, in this area, where our fusing requirements where different than those of the utility.

Field creation of paralleled protective devices is not allowed per NEC 240.8.
There are some switches which are designed to use paralleled individual fuses.

 

[Jraef]

I've seen this done all the time with MV fuses, but the pairs are always joined physically and presumably tested as a single unit. I don't think you can do this in the field. I can imagine the coordination study would be a nightmare. But have you run this by a PE who would be willing to put his stamp on it? That's what it would take if you ask me.



Ah... let that one simmer on the burner too long, others beat me to it.

 

[jim dungar]

I've seen this done all the time with MV fuses, but the pairs are always joined physically and presumably tested as a single unit. I don't think you can do this in the field. I can imagine the coordination study would be a nightmare. But have you run this by a PE who would be willing to put his stamp on it? That's what it would take if you ask me.

Ah... let that one simmer on the burner too long, others beat me to it.

These are not the paralleled fuse prohibited by the NEC.
Yes, they are paralleled fuse elements, but the factory builds and sells them as a single unit.

 

[aelectricalman]

Idont understand how that would apply being a utility pole is far from being a factory unit. Everything on a pole is piece by piece. Anyhow, it turns out, I found a solution to the problem. It turns there are parallelled lines that go down the pole to feed two seperate services. I can just add the 200amp cut outs and fuses at that pole and take 200amps in each direction alleviating the parrallel issue. Thanks for your help guys.

 

[Jraef]

These are not the paralleled fuse prohibited by the NEC.
Yes, they are paralleled fuse elements, but the factory builds and sells them as a single unit.

Right. I said, they are physically joined and (likely) tested as a unit (which as it turns out is a requirement so I now know they are). I wasn't aware the NEC addressed this though. Good to know.

 

[jim dungar]

This is a 14.4kV pole top style, from S & C, which uses paralleled individual fuse elements.

http://www.sandc.com/products/fusing-outdoor-distribution/sm-power-fuse.asp