Question on Fused disconnect

[magicman76]

Lets say I have a 240/480 power source and I need to step it down at the service point. Do I need to install a fused disconnect after the meter can and before the step down transformer or would a non fused disconnect do? I also have a similar scenario with 120/240 power source to step up due to distance and wire size to step back down, do I need a fused disconnect in that scenario? This is for cameras along the interstate. Any references to the NEC would be great. Thanks in advance guys

 

[augie47]

short anser is YES
see 450.3 for overcurrent protection on transformers
and 240.4 for conductor protection.

 

[magicman76]

short anser is YES
see 450.3 for overcurrent protection on transformers
and 240.4 for conductor protection.

Thanks Augie, I guess I'll read those articles and get more familiar with them.

 

[augie47]

I'm sure you can find more specific answers here if you give us details.

 

[magicman76]

I'm sure you can find more specific answers here if you give us details.

Well the 2 scenarios are

1. 240/480 power source to underground pull box (approximately 300 to 1000' depending on how far the power source is since there is like 10-12 different cameras) to the meter can (Since power company doesn't require disconnect before meter) to a fused or non fused disconnect (This is the question) to a 120/240 step down transformer that goes to the panel board with a 2 pole 50A breaker to the camera hub.

2.120/240 power source to underground pull box (approximately 50 to 100') to the meter can to a fused or non fused disconnect (This is the question) to a 240/480 or 600v step up transformer (Approximately 1,000 to 2,000') back to a fused or non fused disconnect (This is another quetion) to a step down transformer to panel board and then to camera hub.

Thanks for the help guys

 

[magicman76]

I believe it requires a fused disconnect but there is a debate going on so I would like to clarify because I'm not 100% sure.

 

[RB1]

Section 230.91 requires the service overcurrent device to be an integral part of the service disconnecting means, or it must be located immediately adjacent to the service disconnecting means. The best way to accomplish this is to use a fused switch.

Also as Augie said, the transformer in each of the scenarios is required to be protected in accordance with 450.3(B).

 

[augie47]

assuming your power source has no protection, then your 300-1000 ft pull would be service. As RB1 states Art 230 says you must have overcurrent protection on the service condutors (230.91), so they would terminate in a breaker or fused disconnect. That disconnect could aslo be your transformer protecton, size per 450.3 Look at 240.2(F) to determine the need for overcurrent protection for the conductors on the secondary side of your transformer. If you are going to a three wire (240/120) secondary, you will need overcurrent potection on that.

In your second scenerio,again 230.91 & 450.3 will require overcurrent protection ahead of your step-up transformer. As this is a could be a two-wire primary/secondary, you might get by without secondary OCP, but your end location will, by nEC, probanluy be classified as a structure and you will need OCP there to protect the feeder. The secondary of that step down transformer will agin need OCP if it's a 3 wire secondary.

For the most part, it sounds like you will need breakers or fuses on the line and load side of your transformers when you take 450, 230, amd 240 into consideration..

 

[magicman76]

Thanks guys I really appreciate the info.