Anonymous Poster
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- Sep 27, 2005
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Ed, while it is always nice to have additional capacity on an electrical service, I certainly do with a 200amp 3 phase service to the shop, and 100 amps to the house, I'm standing by my original comment regarding a 60 amp service to a garage shop.
A couple years ago, when I got a new Amprobe with digital recording capability, I decided to play/learn with it before going out to a jobsite and looking like a fool. My house averages 3 amps on one leg of the service and fluctuated between 2 and 4 amps on the other side for a month. My initial thought was that I had something hooked up wrong, so I hung a pair of amprobes ahead of the current probes, and found the new digital was right on the money.
The biggest current consumers in any residential situation are split phase motors, such as sump pumps and furnace blowers, followed by well pumps and microwave ovens. After a lot of meter reading, I was able to learn most of the power in my house is consumed by those convenient little transformer supplys that serve such items as answering machines and such, along with a FAX machine. Those are the things that run up the total kilowatt hours.
Welders are an interesting load picture, but not huge current consumers. My Lincoln rotarys exibit a load spike as the arc is drawn, and then settle down to much lower current consumption. Transformer welders exibit the same current picture. The cooling fan in my P&H 400 amp TIG machine burns more current than is normally used in the actual welding.
The average garage shop welder is going to run at around 90 to 125 amps out most of the time, and an offhand calculation tells me that will rarely be more than a 20 amp draw on the input. Average shop compressors, nameplate horsepower 7.5 (realisticly 2hp) will usually draw less than 10 amps under normal running conditions, possibly spiking as much as 35 amps on startup. A 9" handheld grinder will rarely draw 10 amps, and a bench grinder is likely to run at less than 6 amps.
Initial startup spikes of inrush current shouldn't be a consideration in service sizing unless everything in the shop will be coming on at the same instant. This discussion isn't about peak shaving or load shedding, it's about a reasonable cost effective service size for a small home shop.
Nameplate amperage ratings while convenient rarely represent true amperage draw any more, since manufacturers have been overrating horsepower for sales. I learned a long time ago that amprobes are a lot more honest than nameplates.
While it is always nice to have a cushion when it comes to power, a cost/benefit analisys has to be done too. There is no point to overbuilding a service.
A couple years ago, when I got a new Amprobe with digital recording capability, I decided to play/learn with it before going out to a jobsite and looking like a fool. My house averages 3 amps on one leg of the service and fluctuated between 2 and 4 amps on the other side for a month. My initial thought was that I had something hooked up wrong, so I hung a pair of amprobes ahead of the current probes, and found the new digital was right on the money.
The biggest current consumers in any residential situation are split phase motors, such as sump pumps and furnace blowers, followed by well pumps and microwave ovens. After a lot of meter reading, I was able to learn most of the power in my house is consumed by those convenient little transformer supplys that serve such items as answering machines and such, along with a FAX machine. Those are the things that run up the total kilowatt hours.
Welders are an interesting load picture, but not huge current consumers. My Lincoln rotarys exibit a load spike as the arc is drawn, and then settle down to much lower current consumption. Transformer welders exibit the same current picture. The cooling fan in my P&H 400 amp TIG machine burns more current than is normally used in the actual welding.
The average garage shop welder is going to run at around 90 to 125 amps out most of the time, and an offhand calculation tells me that will rarely be more than a 20 amp draw on the input. Average shop compressors, nameplate horsepower 7.5 (realisticly 2hp) will usually draw less than 10 amps under normal running conditions, possibly spiking as much as 35 amps on startup. A 9" handheld grinder will rarely draw 10 amps, and a bench grinder is likely to run at less than 6 amps.
Initial startup spikes of inrush current shouldn't be a consideration in service sizing unless everything in the shop will be coming on at the same instant. This discussion isn't about peak shaving or load shedding, it's about a reasonable cost effective service size for a small home shop.
Nameplate amperage ratings while convenient rarely represent true amperage draw any more, since manufacturers have been overrating horsepower for sales. I learned a long time ago that amprobes are a lot more honest than nameplates.
While it is always nice to have a cushion when it comes to power, a cost/benefit analisys has to be done too. There is no point to overbuilding a service.
