Electrical Service Options - Page 1
Forum section: electronics / beginners

author: Poe
author_rank: Frequent Contributor
timestamp: July 15, 2016, 02:40:08 pm
content: Just a few questions about electrical service options in the USA. Our customer is attempting to drive >36kW worth of 120V loads.I'm familiar with the typical residential two phase 240V 200Amp service, but nothing more powerful. I'm assuming factories are wired for three phase with each leg able to supply >200A.Is this correct? What services are typically available in the USA if the common 200A service isn't adequate? Any gotchas that would make what they're trying to do difficult, other than balancing?Thank you.

author: KM4FER
author_rank: Regular Contributor
timestamp: July 15, 2016, 03:39:07 pm
content: If the customer is in a residential area you are probably stuck with 240V but they may be able to upgrade to 400A service. Sometimes you can just add on a second 200A panel. The power company might have to install a bigger transformer and run heavier lines which could result in a pretty hefty bill though. I don't know what I have now but the last place I lived had a 15kW transformer that fed two houses.To get a real answer to your question you need to talk with the engineer at the power company.

author: rstofer
author_rank: Super Contributor
timestamp: July 15, 2016, 03:42:13 pm
content: I doubt that there is a 'standard' ampacity even for industrial users.36 kW at 120V is 300A. This would ALWAYS be unbalanced and I doubt that there is any industrial service that would handle it that way. It would be out of the question for residential.Residential and small commercial might be 120/240V single phase and 36 kW at 240V would be balanced and only 150A. Some residential services are 200A, most are probably 100A and really old services might be a good deal less if the house was built before air conditioning was common.Larger commercial and small industrial will probably have 120/240 3 phase open delta. If the load would work on 3 phase, the current would only be about 75 amps and balanced. Open delta means there are only two transformers on the pole. One is larger and centered tapped to provide 120/240 single phase (for receptacle loads) and the other transformer is smaller and provides only the 3rd phase. In the case of a 3 phase load, it will balance across both transformers.Larger industrial might have 120/208V 3 phase and 30 kW would be about 83 Amps and balanced but the voltage might be too low for the load.Finally, large industrial might have 277/480V or they might take primary service at a higher voltage like 12 kV. Some heavy industrial plants might take very high voltage service at something on the order of 115 kV.So, there is the range of possibilities. I suggest your customer do their homework. If they have any questions, they should contact their utility company.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 15, 2016, 06:10:57 pm
content: It really depends on what you are doing and how you need to meter/control those 120V loads. In one way what you are doing is no different than a small apartment building or strip mall which would commonly have half a dozen to a dozen units each supplied with 100 to 200 Amp service at 120V.Once you have your question well formulated the power companies will be glad to show you the options. The answer will be very location dependent. There shouldn't be a problem in any commercial area and most newer residential areas.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: July 15, 2016, 06:34:04 pm
content: If your customer already has a location, look out the window. If you see three high tension wires atop the poles, you'll likely be able to easily get 3 phase service. I've seen a fair number of 400A split phase 240v services in residential areas driving small apartment buildings, but I don't think they like doing them. The thing is the cost of all the materials shoots up after 200A since those are used for residential stuff and so quite common.But as others have said it depends on location and what your power company is willing to do for you.

author: TimFox
author_rank: Super Contributor
timestamp: July 15, 2016, 08:57:28 pm
content: An example of a utility's practices is contained in the linked document.See page 3 for the usual options for 3-phase power.http://www.600westchicago.info/pdf/comedservice.pdf