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Old 07-08-2011, 09:42 AM   #1
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Electrical Fused Disconnect


I am currently planning to have a local electrical contractor upgrade my 70 amp electrical panel to 100 or more. He has just informed me that the estimate he had originally quote will have to be increased due to my electrical supply company where I live requiring him to install a special devise call a electrical fuse disconnect which must be rated at not less than 56000 volts/amps. Dose this make sense? Such a device has never been in place for the more than 30 years I have owned to property.
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Old 07-08-2011, 10:00 AM   #2
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Electrical Fused Disconnect


Find a new electrician. Hes not being truthful or he does not know what he is doing. First of all, an electrical supply company does not make any rules regarding installation. He may be trying to up sell you on something you may not need. Ask another contractor or two.

Do not take any advice from non-licensed electricians. Make them show you their license.
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Old 07-08-2011, 10:02 AM   #3
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Electrical Fused Disconnect


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Originally Posted by J. V. View Post
Find a new electrician. Hes not being truthful or he does not know what he is doing. First of all, an electrical supply company does not make any rules regarding installation. He may be trying to up sell you on something you may not need. Ask another contractor or two.

Do not take any advice from non-licensed electricians. Make them show you their license.
Sounds strange but I think the OP is referring to the POCO.
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Old 07-08-2011, 10:57 AM   #4
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Electrical Fused Disconnect


Sounds like a disconnect for the POCO out at the pole. More details required as this does not sound like something the electrician would install. Maybe the POCO is installing it and billing you for it through the electrician.
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Old 07-08-2011, 05:46 PM   #5
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Electrical Fused Disconnect


Did you mean "56000 amp interrupt capacity" perhaps? Sounds like the power company is requiring the service equipment to handle higher fault current than usual for residential services. The solution to that is to installed a "fused disconnect" with a 56k AIC rating ahead of the new panel. Are you in a dense urban area?
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Old 07-08-2011, 07:58 PM   #6
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Electrical Fused Disconnect


Call your power company and ask them to provide you with their available fault-current for your location. You might have to ask for their engineering dept.

IF it's over 20,000 Amps, then a standard panel box may not provide sufficient protection.

Let us know your results.
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Old 07-08-2011, 08:01 PM   #7
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Electrical Fused Disconnect


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... an electrical supply company does not make any rules regarding installation. He may be trying to up sell you on something you may not need.....
The OP may be confusing an electrical supply company with a power company. He may not know that the usual term for a supply company usually means a wholesale house.
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Old 07-08-2011, 09:59 PM   #8
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Electrical Fused Disconnect


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Originally Posted by kbsparky View Post
Call your power company and ask them to provide you with their available fault-current for your location. You might have to ask for their engineering dept.

IF it's over 20,000 Amps, then a standard panel box may not provide sufficient protection.

Let us know your results.
That is true I have ran into the same situation espcally with dense network supply and I know once you pass 22KIA it will open new can of worms { that in USA side the French side typically once you get over 14KIA it the same situation as you guys are }

Merci.
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Old 07-09-2011, 12:21 AM   #9
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Electrical Fused Disconnect


56,000 amps is pretty much unheard of for available fault current on a single phase service. I really don't know how you'd get that much.

Suppose the transformer is 167KVA. That's huge, a 75KVA one will feed about a dozen houses, but for the sake of argument, well use a 167.

The full-load current of this transformer is 696 amps.

If the transformer is 4% impedance (Pretty low, most would be 6 or 7%), the short circuit current will be 17,400 amps.

And that's at the transformer, it'll be less at the meter.

A 500KVA transformer at 4% impedance would have a short circuit rating of 52,083 amps. You'll never see a transformer that big installed in a residential subdivision though; it'd feed around 100 houses, and the secondary conductors would be over 1000' long to get to the last house.

I don't see how a disconnect with that interrupting rating would be needed. I get the idea that someone is trying to sell you something you don't need.
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Old 07-09-2011, 04:51 AM   #10
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Electrical Fused Disconnect


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56,000 amps is pretty much unheard of for available fault current on a single phase service. I really don't know how you'd get that much.
It is a crazy high number, but it's at least theoretically possible. As Marc said, it could happen on a network distribution system. That's why I asked if it was a dense urban area.
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