Electrical Service - How Much is Enough?

[Ray Bell]

Foras,

I agree with every thing you say including the Grey Goose, but I cannot go with you to Fox News, and Glen Beck. After all the NFL drafts are going on, and Seattle really needs a quarterback....oops Colt McCoy just went to Cleveland. One pick ahead of Seattle....

[Scott Dallesasse]

[QUOTE=Foras Noir;1406953]I don't respond to posts on posts. But, I can't let this one go.

If you ask a residential electrician what to do, make sure they know they will not get paid if you need to upgrade your service when the in-rush current from your HVAC trips your mains anytime your shop is in use. Seriously, non-shop motor loads will totally wipe out all your shop calculations.

The problem with shops is not FLA (fully loaded amp draw) which is what people on this board talk about day in and day out. It does not matter in shop builds. The problem is in-rush current from low speed (say 1,700 to 3,500 RPM), high torque shop motors. I junked a 7.5 HP 3 phase 208 V air compressor because it pulled 150 A in-rush for 7 seconds every time it kicked. We changed the motor out to a single phase 208 V 5 HP motor frame equivalent and it drew 173 A for 9 seconds. That is not at all uncommon in home shop tools. Anything, I mean anything at all, which is single phase and over 2 HP will have insane in-rush. Please read the reference material I posted.

I'd like to know how you get a 3 phase service for a residential occupancy. Most utilities will not provide this to a residence, even for multi-family properties.

If you want to make sure the service is sized properly, ask to see their load calculations. There are specific places in the code that requires this for the proper OCPD (fuses or breakers) to be sized. This is what is really going to cause the service to need to be increased or not. Just getting the largest one can be just as costly as having to upgrade in the future. Accuracy is a MUST when properly sizing a service, and should not be taken lightly.

[Tom Veatch]

...
You've got a lot of 220v equipment, ... That's good from a "total ampacity" standpoint. But it also requires two slots in the panel (A and B phase) for each receptacle you install, and that is the major consideration. Unless you only want to install one or two receptacles, you're going to need a heck of a lot of slots in that panel for all those 220v receptacles. ...

Difference in local codes?

My shop has several 240v branch circuits, each of which has multiple 240v receptacles and only one breaker for each circuit, certainly not one breaker for "each receptacle". Even has some 4-wire dual voltage circuits with dual voltage NEMA 5/6 - 20 receptacles. All permitted and approved by the electrical inspectors.

Do local codes up in KC prohibit 240v branch circuits with more than one receptacle?

[John Davidson]

I don't respond to posts on posts. But, I can't let this one go.

If you ask a residential electrician what to do, make sure they know they will not get paid if you need to upgrade your service when the in-rush current from your HVAC trips your mains anytime your shop is in use. Seriously, non-shop motor loads will totally wipe out all your shop calculations.

I have worked in industry for 20 plus years as a Electronics/Electrical technician. It would be crazy for any one to apply the same standard to the home/hobby shop. Industrial equipment can and will have all loads on and at full load and in many cases overloaded during some conditions. This will never happen in a home shop unless it is really be used as a bussness and with several employees were the equipment can be all running at once.

The problem with shops is not FLA (fully loaded amp draw) which is what people on this board talk about day in and day out. It does not matter in shop builds. The problem is in-rush current from low speed (say 1,700 to 3,500 RPM), high torque shop motors. I junked a 7.5 HP 3 phase 208 V air compressor because it pulled 150 A in-rush for 7 seconds every time it kicked. We changed the motor out to a single phase 208 V 5 HP motor frame equivalent and it drew 173 A for 9 seconds. That is not at all uncommon in home shop tools. Anything, I mean anything at all, which is single phase and over 2 HP will have insane in-rush. Please read the reference material I posted.Small AC induction motors pull around 7 time FLA at start up. However, this inrush should be over in a secound or two. If your compressor was pulling this inrush for 9 plus secound you sould look at the machnical load and make sure you motor is not under sized or that there is not a problem with the compressor itself. You also refer to 1700 to 3500 rpm motors as being slow speed motors. I would challenge you to find a AC industrial motor that runs faster than 3560rpms when connected directly to the line. To run a motor faster than 3560 requires a drive system of some type. Also Breaker are made to handle inrush current on these small AC induction motors. Breakers are designed to trip uquickly under a short circuit or ground fault but are much slower under an overload condition.

Electricians without actual industrial motor control experience will not know how to even measure in-rush. Make them show you their test gear. Make them do a 48 hour logging run. If their approach is to read the motor plate (which is how residential electricians are trained), you will be back on this board asking how to upgrade the service.

Residential electricians are not qualified for this job. They know nothing about low speed, high torque motors on shop tools. Your power company (if they work like the three I know well) will do the logging and help project your in-rush. They can size the service based on vastly greater experience. They also get no "bonus" income by coming back to upgrade your service.Remember the average house is full of AC induction motors, the frig, the freezer, air handlers, AC compressor units. Do you really think thay don't know what thier doing?

One last time, get the largest service you can. Make sure it is a metered main with at least two feeder breakers (one for shop loads, one for the rest). Everything else will get safer and less expensive.

Your local "time and materials" electrician is the last guy I would ask about this problem. This entire line of argument is valid for all residential contractors. They know nothing about shop infrastructure. I speak from experience. I have about the same equipment in my shop but I have a 2 tom HP with 10kw heat strips for back up. I have a 100 amp service fed from its own meter base. I did the calculations myself as well as the installtion and I have never tripped a breaker. People just don't realize that 100amps is a lot of power for one person to be pulling from the line in a home shop.
Ok - I will go back to my Grey Goose and FOX news channel. I think Beck is on.


Foras Noir
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[Tom Godley]

I guess I read the original post incorrectly -- I thought you were running a sub-panel from the house.

If you are running new service with a new meter just for the shop - I bet you will find the the cost difference between the 100amp and the 200amp service is very small -- making the 200 the way to go.

[Glen Blanchard]

I guess I read the original post incorrectly -- I thought you were running a sub-panel from the house.

If you are running new service with a new meeter just for the shop - I bet you will find the the cost difference between the 100amp and the 200amp service is very small -- making the 200 the way to go.

Actually Tom, we don't know yet. It appears as if we will move into this house in mid-May. It is a pre-owned home, so the current homeowner occupies the house now. As a result, we have not been able to get an electrical contractor to go to the house and determine if the house's service will support a 100 amp sub-panel to the garage. Hope to find out soon.

[Kevin Rector]

This probably doesn't in any way answer your question, but I am in the process of building a shop. I have 200 amp service at my house and I will be running 2 gauge wire out to the house where I'll be installing a full 100 amp subpanel.

In my estimation, for almost any residential hobby shop 100 amps should be substantially more than plenty of juice.

[Curt Harms]

I would look at the maximum number of machines running at one time + lights + any HVAC type loading. I may have 4 240 volt 15 amp machines but I can only use one at a time, plus dust collection. If there are 2 or more people working at the same time, that changes the calculation. It's certainly cheaper to go big enough the first time than having to redo it later, but no need to go nuts.

[Joel Earl]

I run 2 220a tools at a time - like the 2hp DC with the big saw. Lights, music, flip on other 110a's sometimes too. I feed the shop with a 30a sub - thats it. No flicker ever either. If I am running the heat, lights, music, and such in the winter and then kick on the saw and DC at the same instant I have seen a nano second flicker in lighting. But I have on 20 - 8' flourescents too, so at start-up all that stuff must be right there on the edge. Solution is simple - fire up one or other, then the second tool 5 seconds later.

Never happens unless all the heats on - not even with the AC running so I suspect the hog is the heating.

I would maybe have gone to 50a looking back as I might add some extra Boys Toys in future. If I don't I don't - not a big deal when I know manner in how to flip on things.

I didn't say that I have in the main house only 100A service either. 3200sf and 100a and never had a problem. They say balanced load is HUGE. I think that is the real answer