Machine Shop Branch Circuits - Many Loads

[wolfman56]

I have a customer with a machine shop. He has all sorts of milling, CNC, grinding, welding, equipment, etc.
He keeps adding, and adding more machines, and equipment. He has an 800 amp 480 service, that drills down to several different size and type of systems, single phase, three phase, 480, 120, etc.
His shop was originally set up for what he had then with not much room for more load.
I've added more equipment to various systems, each time telling him that he can not use the machines on that feeder at the same time because he'll trip out the breaker.
He always tells me that it's no problem because what machine gets run depends on the job being done, and there is little chance of running too much at the same time.
I get permits, and inspections. Conductors and disconnects are installed as required. Therefore it's always passed inspection. But it's such a complex layout that an inspector has never really looked at whats there. There has never been a breaker trip yet.

An example, there may be two or three 60a milling machines connected to one 60 amp circuit. Only one gets used at a time.

Once again he's called me up and indicated that he's adding more equipment. He wants me to set up more on "shared branch circuits".

Is this approach really code compliant? I can't find a code reference that would forbid this. This is an industrial environment, and he has a shop supervisor on the floor at all times. The supervisor is a machinist though, and not a certified electrician.

Rick

 

[Gac66610]

Have you done a load calculation to see where you're at?

IMO i would recommend a service upgrade (if needed)

 

[Gac66610]

You also have to ask what's going to happen when someone else moves in

 

[wolfman56]

There is so much there it would take all day to calc everything. And he doesn't want to pay for that.

If all were running I don't think the service main would trip. However it's for sure that one or more of the branch circuit breakers that feed panels or transformers, on the floor would trip.

If I calced each branch coming from the main service, I'm sure more load then the breaker would hold. I'ts just not all run at the same time.

RW

 

[wolfman56]

Also, if he moved out, most of the electrical would be removed or redesigned.
RW

 

[Fulthrotl]

I have a customer with a machine shop. He has all sorts of milling, CNC, grinding, welding, equipment, etc.
He keeps adding, and adding more machines, and equipment. He has an 800 amp 480 service, that drills down to several different size and type of systems, single phase, three phase, 480, 120, etc.
His shop was originally set up for what he had then with not much room for more load.
I've added more equipment to various systems, each time telling him that he can not use the machines on that feeder at the same time because he'll trip out the breaker.
He always tells me that it's no problem because what machine gets run depends on the job being done, and there is little chance of running too much at the same time.
I get permits, and inspections. Conductors and disconnects are installed as required. Therefore it's always passed inspection. But it's such a complex layout that an inspector has never really looked at whats there. There has never been a breaker trip yet.

An example, there may be two or three 60a milling machines connected to one 60 amp circuit. Only one gets used at a time.

Once again he's called me up and indicated that he's adding more equipment. He wants me to set up more on "shared branch circuits".

Is this approach really code compliant? I can't find a code reference that would forbid this. This is an industrial environment, and he has a shop supervisor on the floor at all times. The supervisor is a machinist though, and not a certified electrician.

Rick

sounds like most every machine shop i've ever worked in.
'bout 20 years ago, i did work for two machine tool brokerages in the LA area, for about three years...
all their stuff they sold, i'd go do the hookups.

machine shop owners are always changing stuff. constantly.

and everything i've ever learned about getting stiffed on a check, or laundering money for that
matter, has been taught me by machine shop owner.

it's the nature of the industry.

"start the big leblond lathe first, then put the mills online, or you will drop everything...."

bringing the average small machine shop up in the morning is like booting an old pc,
first you load this driver, then that one.... etc.

sit down with him, and explain that you understand he doesn't want to pay for anything,
and you just need for him to understand, that while he's never had a problem before,
he's gonna hate it when someone trips out a milling center, and the part gets scrapped.

i had a mold maker who lost a $25,000 injection mold when he dumped a 5 axis machine.

well, after the paid the mold welder $2,000 to weld it back up, and remachined, reground,
and..... it was only maybe $5k lost.....

you can hook up a lot of stuff to a circuit, and as long as you aren't using it all at once,
all is well....

never did understand how you could make money in a shop without making chips.

relax, make sure there is no risk of shock or safety hazard to personell, and go to the bank.

hopefully the machine that trips out will not be a mill with a magnetic chuck flycutting a
piece of whatever when the power goes off....

 

[ritelec]

Ever put an amprobe on while he was running full load or so?

 

[cadpoint]

One form of studing their service is to get all the monthly bills for the year.

Production technic's and cyling would also have to be considered, next.

I'm sure they have a good accounting of there parts/time ratio pricing and production.

I've seen it said to measure the service at 10:00 and 2:00 when everyone's back at work, but again that's only a part of what's going on for your considerations.

They surely could use some smart wiring on a keyed switch between boxes and a smart controller(logic) to handle the bundling.

What are you going to sell them besides a pipe and some wire?

Eight Hundress Amps is a good healthy amount of service, they would really have to getting it daily to push the limits but we won't know till the numbers are assembled...

 

[ActionDave]

Ever put an amprobe on while he was running full load or so?

I do it all the time. It is enlightening to see how low the amps generally are.

 

[iwire]

You also have to ask what's going to happen when someone else moves in

No, you really do not have to concern yourself with that.

 

[iwire]

220.60 Noncoincident Loads. Where it is unlikely that
two or more noncoincident loads will be in use simultaneously,
it shall be permissible to use only the largest
load(s) that will be used at one time for calculating the total
load of a feeder or service

 

[ritelec]

Would machine-machine..be noncoincidental load as heat-cooling?

Reckon we could twist anything in our mind to work for our needs.


(The ole Harry will be at lunch, and Bill will be in the crapper while Joes on the machine exception)

 

[iwire]

Would machine-machine..be noncoincidental load as heat-cooling?

Reckon we could twist anything in our mind to work for our needs.

I posted the section, it is not restricted to heat and cool.

 

[ritelec]

it is not restricted to heat and cool.

Thanks.......even the heat/cool. You could have heat on in a building for certain areas, yet desire ac in others at the same time............

If you know what the loads are going to potentially be, you could turn a blind eye to make it work for you.

Calculated risk?

 

[kwired]

Ever put an amprobe on while he was running full load or so?

He will likely find that very little feeders or the service are even close to being overloaded.

Thanks.......even the heat/cool. You could have heat on in a building for certain areas, yet desire ac in others at the same time............

If you know what the loads are going to potentially be, you could turn a blind eye to make it work for you.

Calculated risk?

Despite what load calculations tell you this is exactly right.


Reality is not all these machines will draw full load at all times either, some may never be fully loaded.
Reality also is that not all machines will likely operate at same time. It may or may not be predictable which ones will run simultaneously but that is related to the specific facility more than anything that may be published. If it is a facility that can not tolerate shut downs because of overloaded feeders they will not put up with it and change will be requested.

You need to make sure branch circuits are sized properly, but the more machines on a service or feeder the more diverse the load could possibly be, although this is not really addressed in the NEC. Monitoring the existing load however is mentioned when it comes to adding more load.

Hook up some load monitoring devices for a week or a month and you will have a good idea of just how loaded the system really is. Hopefully their production will be at what they call a normal level during this time.

 

[wolfman56]

Thanks for the great replies!

Today I'm going to have them pull up a years worth of electric bills. As far as amp clamping, at no time is everything running all at once, and it changes constantly, so it's hard to get a real picture of what is used. I think the only problem is that he keeps adding more, so sooner or later he's going to forget whats what and end a tripping a breaker.

RW

 

[renosteinke]

All you can do is wait for problems to happen. This guy is going to push, push, push ... until something gives. That's when you get to say 'I told you so' .... and charge him up the wazoo so that the lesson sticks.

 

[ritelec]

Thanks for the great replies!

I think the only problem is that he keeps adding more, so sooner or later he's going to forget whats what and end a tripping a breaker.

RW

And cross that bridge when he gets to it.


What about that whole 80% on the breaker? If the breaker starts tripping more than likely that point would have been compromised for some time......................

Has he had any problems? Has anything been getting warm or HOT...........Do they have fans positioned on the gear especially in the summer months.

Guess your really not going to know where you stand with it till you get the x-rays, mri, cat scan, blood levels, ...................................#'s.

 

[kwired]

Thanks for the great replies!

Today I'm going to have them pull up a years worth of electric bills. As far as amp clamping, at no time is everything running all at once, and it changes constantly, so it's hard to get a real picture of what is used. I think the only problem is that he keeps adding more, so sooner or later he's going to forget whats what and end a tripping a breaker.

RW

Unless the electric bill includes demand data you only know total that was used, but don't know when it was used other than between meter readings. It could all been used in 1 day and then was idle for the rest of month - but was probably used in 8-10 hour periods each week day for the majority of it.

 

[iwire]

All you can do is wait for problems to happen. This guy is going to push, push, push ... until something gives. That's when you get to say 'I told you so' .... and charge him up the wazoo so that the lesson sticks.

What a strange way to treat a customer.