I got a bid to wire machinery shop and storage building. 200 amp 1 phase service. THe customer wants no light flicker whatsoever. The power company I thought was going to bring a pad mount xfmr within a 100 ft of the building. This would help with voltage drop. Now they want set a pot on a pole across the street, run 1/0 triplex overhead to a jump pole, and have me run 225 ft to this jump pole. I have spec'd 250 kcmil to this jump pole. Is there anyway to figure out the voltage drop on all the wires. Will a standard calculation work. The poco says up size the wire accordingly. But when they supply with 1/0 aluminum, I feel it kind of defeats the purpose for us to spend more money on larger wire, when it might not alleviate any problems. Any suggestions or solutions?
Service wire sizing....back and forth with POCO
- Thread starter gk351
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Yes, ask the POCO to bring a padmount transformer within 100 feet of the building like you want. Make sure to tell them you will be paying full cost for this installation.
I bet you didn't talk to an engineer. Probably a service tech in the engineering dept. Ask to speak to someone higher up on the chain.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
assuming aluminum wire you will have a 6.6 volt drop just on your end of the run if the load was 200 amps. What is the actual load.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
The problem with bringing primaries up to a building is having the right of way, most utilities will not bring their primaries without a right of way given to them for future access in the event of a failure, the only other way around this is for the owner to pay for his own transformer and conductors which can be very costly, the other alternative is to size the conductors to minimize as much voltage drop that could be achieved, having 1/0 across the road is only part of the circuit which if short enough can allow you to provide the remaining run with large enough conductors to over come any voltage drop on the remaining run, with motor start up current sometimes it can be impossible even setting the transformer right at the load specially if the POCO sizes the transformer small which is very common, I have seen many 5kva transformers set for 200 amp services and not too un-common for a 10 kva to be set for a 400 amp service, and there is not much you can do if that is all they offer if the voltage drop stays within your states adopted limit which can be +- 10%
Also depending upon the type of lighting installed you can get lighting that does not flicker when the voltage drops such as non-dimming CFL's as they have built in voltage regulation and do not very in light output over a much larger voltage range, I had a very noticeable flicker in my office every time the heaters in my laser printer kicked on and off but since I put CFLs in it no longer happens.
To even figure how large a wire you will need to run will need a few bits of info:
size of transformer set
how long is the 1/0 run
max demand load expected
will you be running aluminum or copper aluminum will be much cheaper and can be sized properly even against copper.
Also depending upon the type of lighting installed you can get lighting that does not flicker when the voltage drops such as non-dimming CFL's as they have built in voltage regulation and do not very in light output over a much larger voltage range, I had a very noticeable flicker in my office every time the heaters in my laser printer kicked on and off but since I put CFLs in it no longer happens.
To even figure how large a wire you will need to run will need a few bits of info:
size of transformer set
how long is the 1/0 run
max demand load expected
will you be running aluminum or copper aluminum will be much cheaper and can be sized properly even against copper.
kwired
Electron manager
- Location
- NE Nebraska
I realize this can vary some from one place to another, but in general if a utility is crossing a private property and is only supplying that particular property easements are not needed. If it crosses a property and supplies another property then easements are needed.
A transmission line or a main distribution line is generally not feeding one property, a service drop that crosses one corner of my yard can not feed my neighbors house without an easement, a service lateral to my business then on via my property to the next door business can not exist without easement because it serves more than just my business.
It does not matter that it is primary voltage or that there is a transformer in your yard, if it only supplies you - no easement is needed even if it is owned by the utility. They generally automatically have easement to access their equipment supplying your property, but to supply other property requires an easement that is documented on the deed to the property,
Average load demand is around 100-120 amps. The person I have been dealing is an engineer and I have dealt with him in the past. If I'm able to overcome the wire drop from the poco 1/0 how do I figure it. To me, it doesn't make sense. If I start out with 1/0, how can my voltage increase or overcome the initial 75 ft of wire from the POCO by increasing my wire.
The reason the owner is worried about light flickering is because he has a current shop that is setup similar and the group who wired it ran 250 kcmil ALUW to the meter base and 4/0 ALUW from the meter base to the load center (violation). His meter base is probably 225 ft from the pole. So he is just wanting me to be proactive and try and prevent this wih his new shop.
The reason the owner is worried about light flickering is because he has a current shop that is setup similar and the group who wired it ran 250 kcmil ALUW to the meter base and 4/0 ALUW from the meter base to the load center (violation). His meter base is probably 225 ft from the pole. So he is just wanting me to be proactive and try and prevent this wih his new shop.
kwired
Electron manager
- Location
- NE Nebraska
Without looking it up I'm pretty sure 4/0 aluminum is good for 180 amps @ 75 deg C. Allowed next higher overcurrent device is 200 amps. Unless your calculated load is 181-200 what is the violation?
You can not overcome any voltage drop that already exists ahead of anything you install. 75 feet of 1/0 overhead is not too bad, and is in fact pretty common to run even farther than that on rural services around here. They will provide most anything I ask for here but if I wanted that line heavier or transformer closer the customer will likely have to pay for it, sounds like they are not too willing to do so even if customer pays.
The way I was taught, 4/0 ALUW is for residential services only. Besides, If I have a 200 amp ocp, IMO it going to have 3/0 CU or 250 ALUW. After you leave a Job, how can you account for future load increases that are unknown. I say it's a good practice for what I have been taught.
Besides, unless the crew that wired the original building was short 15' of 250 kcmil, it seems dumb to convert to 4/0. IMO
Besides, unless the crew that wired the original building was short 15' of 250 kcmil, it seems dumb to convert to 4/0. IMO
kwired
Electron manager
- Location
- NE Nebraska
Do you use 500 copper for 400 amp conductors? Many people do. It is only rated for 380 amps next size overcurrent device is 400, which makes it fine as long as actual load is not over 380. Where they get into trouble with 500 is when they try to parallel 3 sets to get 1200 amps. Total conductor ampacity is only 1140 and when over 800 amps you can no longer use next higher overcurrent device.
You can also parallel 250 or 300 copper and protect with 600 amp overcurrent device as both would be more than 500 amp conductors but next size device is 600.
You can run any size conductor you wish as long as its ampacity is more than the load less any needed adjustments, overcurrent protection is a separate step.
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