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Rotary Phase Converter Tripping Breaker

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Forum topic by Ben posted 12-14-2015 02:33 PM 539 views 0 times favorited 11 replies Add to Favorites Watch
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Ben

267 posts in 2320 days


12-14-2015 02:33 PM

Not sure if this is the right forum, but I’m hoping some of you are electrically very savvy.

I have an Arco Electric phase converter. It’s rated to power a 5hp motor, with a combined 20HP load.

I have it installed on a 220, 30amp breaker feeding a sub panel, with another 220 30 amp breaker in it. All wires are 10gauge.

I am using it to power a 5hp Powermatic Planer. The motor tag says it draws 13amps at 220v, which is what it’s wired for.

What’s happening is, I’ll turn on the converter, wait a few seconds (while I walk over to the planer), and about 9 times out of 10 when I fire the planer, just before the motor gets up to full speed, the breaker will trip – the breaker in the main panel, not the actual breaker to the RPC.

I’ve tried running the RPC for about 20 minutes, thinking it was a cold issue, but the planer still tripped it. It’s been in the 40s/50s here too, so it couldn’t be an issue of cold grease or something.

So, is the motor somehow drawing more than 30 amps? Or do I have a defective breaker?

Eventually, somehow, I get the system working, and then it’s fine for repeated on/offs.

Appreciate any help.

Thanks.


11 replies so far

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Nubsnstubs

826 posts in 1193 days


#1 posted 12-14-2015 03:44 PM

I know there are a lot more people more knowledgeable than me, but I always thought that phase converters needed to produce at least at least 20% more than the motor it will drive. You are producing power for a 5 hp motor with a 5 hp phase converter. It won’t keep up, so the trips are happening. Please, more intelligent input needed…......... Jerry (in Tucson)

-- Jerry (in Tucson)

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Ben

267 posts in 2320 days


#2 posted 12-14-2015 08:56 PM

Thanks Jerry.
I don’t know what the HP of the converter motor is, but it’s rated to power a single 5hp motor, and combined 20hp – says right on the tag.

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MrUnix

4221 posts in 1662 days


#3 posted 12-14-2015 09:00 PM

HP is a meaningless term when it comes to sizing equipment… what is the model of RPC you have, and what is the FLA rating on your planers motor?

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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Ben

267 posts in 2320 days


#4 posted 12-14-2015 09:02 PM

I have the Arco Electric model A.

According to my planer’s motor, the FLA is 13.

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MrUnix

4221 posts in 1662 days


#5 posted 12-14-2015 09:10 PM

Uggg.. the Arco site is vague on specs… but it does say that 5hp is the max, and indicates that if your motor has a low power factor rating (among some other conditions), you should size it up to the next larger unit (Model R). Although, if it works fine sometimes, and not others, you might want to contact Arco about the problem and see what they have to say about the issue. Is this a new setup and/or a new RPC?

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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Ben

267 posts in 2320 days


#6 posted 12-15-2015 12:36 AM

Thanks Brad.
This is a unit I purchased used and I believe it’s from the 70s. PO hadn’t run it.
I need to figure out how to meter it and check the load when I fire up the planer, then I’ll report back.
Thanks

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MrUnix

4221 posts in 1662 days


#7 posted 12-15-2015 12:46 AM

You could probably still get in touch with them to see if they might offer any advice… wouldn’t hurt.

If things don’t work out though, another option would be to get a VFD for about $200… it would give you several benefits over an RPC, but would be for the single machine only… if you have the RPC so you can run multiple 3 phase machines, it might not be as attractive.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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Ben

267 posts in 2320 days


#8 posted 12-15-2015 01:06 AM

Yes, I have called them and they basically just told me to meter it.

I agonized at length over VFD vs. RPC. For a 5hp/13 amp motor, the VFD gets insanely expensive, but they are out there used.

And now I have a 3.5 HP bandsaw I’m restoring that is 3 phase so I really want to get this working.

Thanks for your help man.

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MrUnix

4221 posts in 1662 days


#9 posted 12-15-2015 01:29 AM

I agonized at length over VFD vs. RPC. For a 5hp/13 amp motor, the VFD gets insanely expensive, but they are out there used.

For that motor, you could easily use something like the FM50-203... for under $200. Those motors rarely, if ever, see FLA, and the VFD can sustain up to 150% overcurrent for short periods of time, and will just go into overload mode if you push it past it’s limit for too long (and you just need to hit the reset button and continue on). Take a look over at the OWWM or PracticalMachinest sites for lots of examples of them being used for that application.

But if you can get your RPC working, that obviously wouldn’t incur any additional costs :)

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

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REO

889 posts in 1537 days


#10 posted 12-15-2015 11:16 AM

Not sure what is in your particular RPC some have a current sensing relay. they can get set improperly. I have built several from scratch. the first one many years ago was still in use til last year. On an RPC the capacitors drop out when they are up to speed, If they are held in the circuit the Rpc will not get to full speed as they are meant for start up. some of the more complicated ones use a second bank for balancing the voltage on the legs. Check the voltage on the legs at idle without the planer hooked up and the amperage on the input. for light loads Most RPC have no trouble with three times the size of the converter motor. I have run 2 five horse and a two horse in a production environment all day with out tripping out or harming any of the motors.

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TopamaxSurvivor

17669 posts in 3139 days


#11 posted 12-16-2015 06:35 AM

If your breaker is properly installed and there are signs of heating or arching on the connections or bus bar of the panel, I suspect it is a defective or undersized breaker. What brand are your breakers?

5 hp on 220 volts single phase normally requires #8 wire and 60 amp breaker unless the manufacture’s instructions say different.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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