How would one go about making sure a service is able to handle another motor load?

[Mr. Spinosa]

I am a licensed commercial electrician and I am working on getting my administrator's license. I would like to know from another professional how they might go about finding out whether or not another motor load might be installed in a commercial installation without recalculating the entire load for a building. - For example: A customer asks you to install a new motor conveyor and he shows you right where he wants it. Let's say there is a sub panel close by and you want to add it to that sub panel. - Is it really necessary to find every load attached to that sub panel and recalculate everything and make sure it all falls within code? How does a professional approach this? All or most of the work I have done while working for others has been engineered or "given to me" by my superiors. But as a small contractor I anticipate running into this type of scenario and I would like to see if I can get some input from another professional on the best way to approach this without making a big project out of a small one. - Any help is appreciated and thank you in advance.

 

[petersonra]

I suspect the vast majority of people would just add a small load like this and not give it much thought.

 

[rbalex]

The most common approach is 220.87 Ex.

 

[rt66electric]

rule of thumb

rule of thumb

I suspect the vast majority of people would just add a small load like this and not give it much thought.

Goto the main panel or transformer and stick your thumb on it. If it not warm it is not loaded enough. Sit on the Tranformer , If it is warm enough to keep your hinney warm a coold day-- then it is loaded about right. If the transformer is hot enough to keep you coffee cup hot--- then you might consider making some actual measurements.

 

[ceb58]

Goto the main panel or transformer and stick your thumb on it. If it not warm it is not loaded enough. Sit on the Tranformer , If it is warm enough to keep your hinney warm a coold day-- then it is loaded about right. If the transformer is hot enough to keep you coffee cup hot--- then you might consider making some actual measurements.

Now if we could get a code change

 

[Cow]

Goto the main panel or transformer and stick your thumb on it. If it not warm it is not loaded enough. Sit on the Tranformer , If it is warm enough to keep your hinney warm a coold day-- then it is loaded about right. If the transformer is hot enough to keep you coffee cup hot--- then you might consider making some actual measurements.

I like this reply!

In all seriousness, if it's just a few horse and the panel doesn't look loaded, just add it. If it's a pretty good sized motor and you're starting it across the line, it might be a good idea to do a little investigation before you start blinking the customers lights....

 

[rbalex]

If we were making yogurt the old fashioned way, ?thumb degrees? would be a recognized technique. (It was a measure of how long you could keep your thumb in the brew to achieve the right temperature).

However, the OP asked how a professional would do it without tracking down each load and computing the result. As practical as the alternate proposed method seems, 220.87 is the only NEC compliant method. I have used the Exception many times.

 

[Mr. Spinosa]

Thank you, so much. I really do appreciate your answer.

Thank you, so much. I really do appreciate your answer.

The most common approach is 220.87 Ex.

I just want to say thanks for your answer... I'll have to delve a little more into that part of the code. - I have to agree that most of the time we might not want to give it too much thought; I'll have to learn how to balance all of that out. (Even the funny remarks posted by others were helpful in that regard!) But, I think I've gotten a good sense of where to begin if the case be that it is worth a little more investigation. - Thanks again.

 

[hurk27]

Goto the main panel or transformer and stick your thumb on it. If it not warm it is not loaded enough. Sit on the Tranformer , If it is warm enough to keep your hinney warm a coold day-- then it is loaded about right. If the transformer is hot enough to keep you coffee cup hot--- then you might consider making some actual measurements.

Are you from Alabama

 

[Mr. Spinosa]

Thanks for your input.... Sounds like a good approach.

Thanks for your input.... Sounds like a good approach.

I like this reply!

In all seriousness, if it's just a few horse and the panel doesn't look loaded, just add it. If it's a pretty good sized motor and you're starting it across the line, it might be a good idea to do a little investigation before you start blinking the customers lights....

Just wanted to say thanks for your input. - Sounds like a very reasonable approach.

 

[GUNNING]

options

options

couple of choices

Get engineering by a professional with plans.

Or

Do the load calculations yourself using the added load calculations from the code book. It would be an opportunity to do a survey of the panel(s) and or service and redo the panel schedule. Might find several outlets that need upgrading or circuits in need of changing or even a whole new sub panel and feed. That is what the engineer would be doing. If the numbers show that you need a new service you would be negotiating from a more knowledgeable position. This service would benefit the customer in many different ways and tell them you know their electrical needs up close and personal.

Or

Tell the owner you would put in the added circuit for the motor loads and try the smoke test. If the magic smoke comes out there would be more work required like maybe a new service or sub-panel upgrade. If they don't like these options pay for either option one or two.

Options one and two are paid for service options, three is a WAG. More experienced electricians can do the WAG with knowing what the loads are, do some mental gymnastics, and calculate the expected ampacity of the sub-panel. Handymen get an extension cord and plug it in, ty wrapping it to anything that looks like it will stay put.

Make your decision on what your customer will accept. They are ALWAYS right.:happyyes:

 

[Mr. Spinosa]

Ahhh yeah!... pretty funny. I have to give you a hand. You got me laughing.

 

[petersonra]

I think most of us could take a quick look at a system and decide whether what someone wants added can be safely added without going through hundreds of dollars worth of calculations and field investigations.

Any substantial load (like a 100 hp motor) being added is going to require more work anyway, so the added cost of crunching the numbers and doing the field work up front is less of a problem.

Adding a single 120V outlet to a lightly loaded panel requires less thought up front.

My guess is if you have to think about it for more than about 15 seconds, you probably need to do the field investigation and calcs.

 

[growler]

I suspect the vast majority of people would just add a small load like this and not give it much thought.

Much of the times, yes.

It really depends on the size of the motor and the size of the sub panel. If the sub panel is a little single phase 208V 100 amp then I will give it more thought than if it's a 400 AMP three phase.


Many times you can just look at the panel and see that it's not loaded at all to start with. At other times you think this darn thing is already overloaded. :slaphead:

 

[Joethemechanic]

Hook up some of these, don't forget to change the charts. Make sure if they are doing something usual they let you know.

 

[Wes Smith]

What's wrong with just throwing a clamp meter on it, see what it's drawing, and go from there.
If its too close then investigate further.

 

[iwire]

What's wrong with just throwing a clamp meter on it, see what it's drawing, and go from there.
If its too close then investigate further.

The only thing wrong with that method is it is a code violation.

 

[Wes Smith]

iwire, I hear and respect what you're saying. I just think that "sometimes" its ok to just be practice with this stuff. If its too close for comfort then do the necessary work.