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Which Heater for a DP? (Cutler Hammer Manual Starter)

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Uglydog

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#1
Can anyone coach me on which heaters I need for a Cutler Hammer Manual Starter NEMA 1 (pic below)?
Based on http://www.electricalmaterials.ca/ch_heaters.htm
It appears as though I need to know if this is an open or enclosed Cat....
IMG_1652.JPG

Here is specifically what I'm thinking:
Note: I want this to be this to be safe and appropriate?
This Manual would switch two 3hp 3ph motors.
Each would have it's own down line switch.

The Clausing DP is powered by a 3ph 3hp motor drawing up to 9.2amps at 230v (pic below).
Eventually I want to feed this through a F/R drum switch.
IMG_1650.JPG

The WT DP two speed motor already has a two speed F/R switch (motor pic below).
At 3hp she supposedly draws up to 8amps.
I'd add a second set of heaters to protect the low speed after the low speed switch.
IMG_1661.JPG

Please note that one motor pulls the 9.2 and the other 8.0.
I'm thinking of installing heaters to cover the 8.0.
If I'm pushing a DP hard enough to use all 3hp I'm overworking the drills.
Worst case I might have to let the heaters cool. It shouldn't hurt the motor. Is this correct?

Yes, I'm aware there might be better ways to do this. Such as two F/R magnetic starters.
However, this manual starter was gathering dust on the shelf, and the two speed motor is already wired with a two speed F/R drum switch.

More parallel thread here: http://www.hobby-machinist.com/threads/thanks-to-hm-for-the-clausing-dp-restore.61569/
There was a thread I started last spring when I was thinking of using a VFD. However, I'm thinking for the times I need to drill large enough to warrant that slow of a speed (below 200) I can use the Cincy Toolmaster 1D 40taper mill and it's power down feed.

Thank you all for your ongoing assistance and redirection.

Daryl
MN
 
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Technical Ted

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#2
As far as the heaters go in contactors like this, the windings of the heater coil go around solder pots. In the case where the motor/circuit draws more than the rated current, the heater coils heats the solder pots to the point where the solder melts and this allows the gear/shaft in the solder pot to revolve tripping the overload. So, you'll have to look up the correct heater size for whatever amperage you consider max that you want to allow before tripping.

If the motors have built in overload protection it's not as big a deal because they will take care of themselves. Otherwise, a motor should always be protected and sometimes the correct sized fuses will do the job. You'll have to look up what sizes to use to cover not only running amperage but in-rush (start up) amperage as well. Rough rule of thumb is the in-rush is twice the full load current draw. Typically, slow blow fuses are used to handle the startup current.

If would probably be best to protect the smaller motor. This means no full load for the bigger one, but as least they will both be protected. I personally would not want to have to continually allow my heaters to cool off to keep the motor running. They are doing their job of protecting your motor by getting hot. I've seen people put fans or air hoses on devices like this to keep things running... NOT a good idea!

As far as enclosed or open, it depends on whether the contactor is inside a self contained small box. If it's in a large cabinet it is considered open.

I attached a CH heater selection chart I found on line, but not sure if it's the correct one for your motor starter. I'm sure you can easily fine the correct one if needed.

Good luck,
Ted
 

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Uglydog

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#3
If would probably be best to protect the smaller motor. This means no full load for the bigger one......
As far as enclosed or open, it depends on whether the contactor is inside a self contained small box. If it's in a large cabinet it is considered open. Ted
Helpful data.
Thank you.
Daryl
MN
 

Technical Ted

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#4
I forgot to add, the reason for the difference between open and closed is how open the contactor (and it's heaters) is for cooling. Open, more air and cooling. Closed, less possible air flow and cooling and the heaters will get hot enough to melt the solder pots more easily/quicker at the same current draw, so in this case, you would need higher rated heaters for the same current limiting.

Ted
 

Linghunt

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#5
Open and closed also has a lot to do with finger guarding and safety barriers. The finger safe are pretty nice for clumsy technicians. But then again all can slip and touch something hot.

I recall wiring up a couple old open contactors like that in a small box for a water pump in a water spring. One of them was for the pump and the other was on all the time to generate heat and reduce condensation and corrosion inside the box. --Rainy Redwood forest area--
 

Ulma Doctor

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#6
10 amp (FH40{9.5-10.4Amps} or FH41{10.41-11.30Amps}) heaters will be sufficient for your needs.
the FH40 heaters will cut out earlier, but there is not much difference- 1 amp, not critical for a DP motor

if you wanted to have the heaters come in early you could go with a FH38 or FH39
but you may make the heaters fail at a more rapid rate.

when the heaters are too close to operating range amps, they heat up time and again.
this thermal contraction and expansion ends up creating resistance in the heater over a period of time.
pretty soon the heater no longer retains the original resistance value and doesn't cut out as originally designed.
if left untreated, the heater will become so resistant that it actually becomes a fuse.
the heater wire will break and no power will flow through that pole of the overload.
at that time if the overload relay is operating correctly, you should not be able to operate the equipment.
the fault should interrupt the contact coil holding circuit leaving no power for the magnetic starter coil to operate
 
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