Hi All!

I currently have an old 40 amp service in my pre-war condo. We are allowed to run BX securely attached for a new service.

The distance is 250 feet. I am looking to get a 100 amp service. What size BX cable should be used for this? Do they make BX large enough for a 250 foot 100 amp service?

I am also wondering what wire it should be, copper, aluminum?

Any help before I speak with the electrician and board is greatly appreciated.

Thank you!

Tim

tkrussell

You need to consult with your electrician, as this is an odd situation.

A 100 amp panel will need to assume the maximum load is 80 amps, and a 100 amp feeder at 250 feet needs to deliver no less than 3% voltage drop.

This will need either #3/0 copper or 250 MCM aluminum wire.

Glaesemann

I was just trying to prepare before I spoke with my electrician and my condo board.

My electrician quoted 2/3 BX.

$2000 in BX alone !!!

Yikes!

Job starts today. No choice I guess.

Thank you.

Tim

tkrussell

Yes I know that copper is expensive, aluminum for feeders is much less.

So someone is running 250 feet of #2/3 copper cable for a 100 amp serivce?

I will be very interested in the voltage drop.

Mind you, if the electrician measures the voltage when he is done, with no or little load, the voltage reading will probably be OK, the voltage drop will become evident as more load is applied.

Glaesemann

He played this fact down. He said it only mattered if you had "voltage sensitive" items on the load.

I told him i DO have voltage sensitive items on the load. I am an audiophile and would love to see as little voltage drop as possible.

He assured me it was only an issue with sensitive computer equipment.

I am glad you mentioned this. I am going to ask some more questions.

He didn't come today after all this, because they had an emergency job.

Would conduit and 2/0 be the correct wire method to avoid voltage drop?

Thank you!

Tim

tkrussell

If #2 copper is 250 feet long, with a reasonable load of 50 amps, the voltage drop will be 4.9 volts, or 4.8%.

Maximum reccommended voltage drop for a feeder is 3% to the distribution point, or the breaker panel.

#2/0 will offer 2.5 volt drop (2.1%) for the same load. An 80 amp load will result in a 3.25% Vd.

This is acceptable if the branch circuit wiring is not too long, as the final Vd at the outlet should not be more than 5%.

If this was my job I would be selling you #2/0 Aluminum in PVC conduit (if PVC is allowed in your area) The Vd is still a bit high for 80 amps, but here is where what are the chances of a full load being applied. For a 50 amp load the Vd is perfect,2%.

What does the local electrical inspector say about this?