# Allen Bradley Type 0, Heater Question



## invisabledog (Mar 1, 2015)

I need to know what heaters to run in my original switch. I had a 440v only motor rewound to 220/440. I'm running it on 220 3ph through the original AB switch. It runs awhile then quits. I can hear a click coming from the switch. I'm guessing I need bigger heaters to run the 220. It currently has n17's. Am I correct? If this is the case and I need to upgrade the heaters, which ones do I need? I don't know what the amp draw is on the motor. It was rewound to a modern 9 wire configuration and it is a 2hp motor. Below is the switch as it was wired for the original 440v.


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## JimDawson (Mar 1, 2015)

Good question.  Without knowing the amp draw of the motor, it's impossible to size the heaters.  Having said that, the amp draw should be twice the 440V draw, and given that you have N17 heaters installed.  So based on that information, it looks like a N24 might work.  But check the amp draw to make sure.

http://literature.rockwellautomation.com/idc/groups/literature/documents/td/815-td002_-en-p.pdf


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## UncleRuss (Mar 2, 2015)

WOW!  You indeed have an very old antique there.  They were even throwing those away when I started in the trade long, long ago.  Go to a NEMA chart or from a code book and find what a 2hp 3ph motor is supposed to draw (6.8 amps).  Then size the heater from the chart listed as single unit in small enclosure.  Find where the chart crosses 6.8 amps and there is your heater size.  You can read the tab on your existing heaters as only being of 1/2 value needed.

You can not "measure" your motor as you do not know what full load is and if you do increasingly load the motor to full value when do stop adding load? 

Allen Bradley was kinda smart in the design of their heater being so universal and still in use for damn near a hundred years!


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## invisabledog (Mar 2, 2015)

It's old but cleaned up well.  My original motor before the rewind was rated at 2.7 amps.  I doubled that for the 220v and came up with needing an N24 at 5.7 amps. I checked the rating of the N17's that are in it and they are 3.01 amps.  I decided to go up one step and ordred a pair of N25's  which are 6.38 amps.  I'm hoping I won't be loading the grinder to need more than that.  If they aren't enough I'll go one more step up.


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## Dawner (Mar 2, 2015)

The rule of thumb for electricity is when you  1/2 the voltage  you double the current. what every heaters you ran at 440 v is two times.  My main concern is: Are you still using the old existing wiring running to this equipment  ?  That wire may need to be increased in size depending on the length of the run.  Oh sure it will run fine at first,  then you put it under a load then it stops or acts sporadic .  Worst case  then it becomes the fuse for your new torch.  OR.... plan "B" or decrease your deductible and raise you benefits on your fire insurance policy. 

just saying Dawner


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## Vladymere (Mar 2, 2015)

I would recommend replacing the overload protection.  What you have, with appropriate heaters will work but it is only providing protection on two legs, not three, as the current crop of NEMA overload protectors would.

Vlad


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## jim18655 (Mar 2, 2015)

The motor lead on the right must go through the knockout on the left or you risk creating inductive heating. Will it cause any damage? Probably not, but it's the right way to wire something. 
FYI- The charts in the NEC are for sizing the branch circuit not the motor overload protection. Motor overload protection is from the motor name plate data 430.6 (A)(2). I would use the data plate from the original motor or call the re-winder for overload recommendation. He should know if anything changed.
Can you find an amp rating or size on the switch?  Even if the wires are 14AWG they would handle a 2HP motor on 220V but the switch may be too small.


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## ironmonger (Mar 2, 2015)

This isn't being run from a VFD is it. I saw the earlier post regarding the grinder and was curious if this was the same motor. 
I only mention this because you can fry your VFD if you interrupt the VFD to motor leads with a switch or a disconnect. 

paul


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## invisabledog (Mar 2, 2015)

The motor is being run with a rpc and all supply wires have been replaced.  The motor wires all enter through one knockout and the supply through the other.


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## ironmonger (Mar 3, 2015)

Ok, just checking...
I have nothing against RPC's and have used them in the past. So no bias here, just a thought... it would be interesting to check each leg of the RPC feeding the motor. By their nature the phases aren’t balanced perfectly, so I wondered if the slight imbalance might be affecting the heater current. 

All the usual cautions about clean solid electrical connections apply. 

paul


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