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Customer runs a machine shop out of his garage at home. He currently has 1, 10 hp. phase convertor on the service. He wants me to install 1 additional 10 hp. phase convertor for a new machine he wants to purchase. I'm concerned about him starting them at the same time and tripping the main breaker or adding the additional phase convertor overloading the existing service.
 

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Customer runs a machine shop out of his garage at home. He currently has 1, 10 hp. phase convertor on the service. He wants me to install 1 additional 10 hp. phase convertor for a new machine he wants to purchase. I'm concerned about him starting them at the same time and tripping the main breaker or adding the additional phase convertor overloading the existing service.
Load calc time.

I would call the manufacturer on the load inrush.


Have you asked poco about 3 phase? If he is running enough to warrant a larger service that will be the cheaper route to go unless poco has no 3 phase near by.
 

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Time delay relay?.

I agree with post above 100%. But was wondering, what if you used a 10- second time delay relay to control one of the contactor coils?? Because like you said if they both started simultaneously, your talking almost 160a inrush (based on 300% of motor rating) plus whatever else you have running. If I'm wrong about the inrush, someone please chime in because I believe I seen that formula on here.

Or buy a small generator lol.
 

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How big is that machine is ,? ( x of hp ) and i am stronly advise to check with POCO.. To see if they can provide 3 phase service ..i know the poco in wis will only give you wye system ( 208Y120 ) but delta that i do not know what the POCO will give delta for resdentail...

However the biggest isusse will be exsting transformer size...

I know my 15 hp commpressor was weired on 208 that dtaw about 45 amps but i move it and rehook on 480 volts it ran about 22 or so.

Otherwise you can hevay up to 400 amp single phase..( check the poco for their trans hevay up too )

Get load demand caluacation so you can see where ya at..
 

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Customer runs a machine shop out of his garage at home. He currently has 1, 10 hp. phase convertor on the service. He wants me to install 1 additional 10 hp. phase convertor for a new machine he wants to purchase. I'm concerned about him starting them at the same time and tripping the main breaker or adding the additional phase convertor overloading the existing service.
I see less concern about people that want to install an electric tankless water heater that has a 22kw nameplate
 

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The problem with asking for a 3 phase service on a residence, is that they don't realize that it will come with another meter, a Demand Meter, and they will start paying demand charges on top of their actual usage. I never recommend that for someone who is used to residential service rates, it's often a BIG shocker and they blame the electrician for talking them into it.

Inrush on each of the 10HP RPCs will be 600% of the single phase FLC based on the HP rating. So for 10HP 240V, that's 55A FLC, so the starting current will be 330A for each one, 660A if they start simultaneously, albeit only for a second or two. A 200A service will likely handle that to be honest, but if there is a lot of other stuff connected at the same time, it's a crap shoot.

I would add a delay start timer to one of them. Just 2 seconds would probably be enough. Better yet, make it so that each one has to be started manually with a 3 wire control scheme so that if power fails, they can't re-start automatically. Then put the start buttons out of arm's reach of each other, so he HAS TO walk from one to the other. That forces a staggered re-start after a power loss. Safer that way too.
 

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Are these those automated machines that materials are inserted and they run for however long it takes to produce a run of parts or are they something that someone has to stand and actually interact with? I could see the concern for another of the first type, but a couple of lathes for instance, he can't likely be at more than one machine at a time.
 

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He's got the wrong thinking.

Lathes -- in particular -- work perfectly fine with even cheesy Chinese VFDs.

No-one ever starts an engine lathe under load.

Indeed, a hobbyist is never going to tax the motor.

 

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I helped set up a really fancy wood shop for a friend of mine who was worried 200 amp wasn't enough, until I reminded him he could never use more than one machine at a time because he works alone. I could see where maybe there'd be trouble with a couple automated units.
 

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Customer runs a machine shop out of his garage at home. He currently has 1, 10 hp. phase convertor on the service. He wants me to install 1 additional 10 hp. phase convertor for a new machine he wants to purchase. I'm concerned about him starting them at the same time and tripping the main breaker or adding the additional phase convertor overloading the existing service.
What machine is he getting? Is it a metal shear with a big flywheel, lathe or CNC machine? Each of these loads have different requirements. For example we built a phase converter for a CNC metal press that had a huge flywheel to get spinning. Most CNC machines have very sensitive electronics to account for.

Phase converters are also built very differently. Depending on how they're designed it may be drawing close to full load current just sitting there idle and ultimately self destruct if there is no load on it. My Dad designed a phase converter years ago that is probably about the best design I've seen. We have been building them for years. We have a lot of them out there in this very application. One shop in Waterford, PA has close to 10 of them sitting side by side. They start easy, provide a very balanced three phase power and are very efficient. Case in point - we recently sent a kit to Indiana for an Electrician to build a 100 HP phase converter. He put everything together per our instructions and he just called us last week to tell us that running with no load it only drew 9 amps.

My Dad would be happy to help you out. Just PM me and I'll give you his number.
 
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