Burning pool motor connection

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PapaGreg

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A motor connection on a 7 1/2 HP pool pump motor is burning up weekly. The motor runs continually drawing approximately 20 amps per leg three phase 240 volts. The motor leads are connected with Burndy BIT-4 connectors. We replaced the burnt connection, the BIT-4 connector melted, yesterday and today the insulation on the new connector is brown and getting a charred look to it. Connector new has a clear insulation covering. Plastic marking tape,on the wire feeding the motor, 3/8" from the connector is not affected. The other two connections are good. The motor connections were left out of the motor wiring box overnight. Any thoughts on this?
 
PapaGreg said:
A motor connection on a 7 1/2 HP pool pump motor is burning up weekly. The motor runs continually drawing approximately 20 amps per leg three phase 240 volts. The motor leads are connected with Burndy BIT-4 connectors. We replaced the burnt connection, the BIT-4 connector melted, yesterday and today the insulation on the new connector is brown and getting a charred look to it. Connector new has a clear insulation covering. Plastic marking tape,on the wire feeding the motor, 3/8" from the connector is not affected. The other two connections are good. The motor connections were left out of the motor wiring box overnight. Any thoughts on this?
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About 90% of the time, burnt or heated connections are due to loose connections.
 
Try this from T&B
https://www.tessco.com/product/437469
Or the same from Burndy Pentarox E. Penatrox E is in a squeeze bottle I carry one in my tool kit
Its copper in an oil solution.
I used to work on police cars with high draw lighting, the 30 AMP ATC fuse holders would melt. Penatrox E on the blades and the problem went away.
I use Penatrox E on threaded connections, wires in terminal lugs. Its a miracle product..but messy. "It gets home before you do"
This product has cured overhead connections on motor starters with continuous loads (65 amps on a 4 AWG)
 
Burndy now has Unitap "flex" connectors - designed for fine stranded conductors. Basically has a pressure plate that clamps the conductor rather than direct contact to the set screw.
 
240 3ph, 20A each, thats ~14kW
Which is not a 7.5hp (~5.5kW) motor

Please explain.
 
ptonsparky said:
I haven’t seen those yet. Won’t either until all the old stock is sold.
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Do you do business with 3-E? they have both, in the Norfolk store anyway. But only certain ones, the ones you really want are always in another store the day you want them;)
 
jumper said:
Check your math.
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I thought I did.

240v(rms 60Hz) 3ph, 20A per leg (measured)
240 x 20 x 3 = 14.4kW

even under 240 x 20 x 0.9PF x sqrt3, = 7.7kW, more than the motor rating?
 
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jumper said:
7.5HP x 746= 5.5 kW

Motor chart FLC for a 7.5 240V 3P motor per NEC 430.250=22A

Seems normal.
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yes, but the RMS measurements were 20A per leg. 240v per leg, so its a 4 pole delta?
 
FionaZuppa said:
I thought I did.

240v(rms 60Hz) 3ph, 20A per leg (measured)
240 x 20 x 3 = 14.4kW

even under 240 x 20 x 0.9PF x sqrt3, = 7.7kW, more than the motor rating?
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We are assuming that this is a 240V delta, so the voltage to neutral is 139V. And 139V x 20A x 3 = 240 x 20A x sqrt(3).

That is another simple way of deriving the sqrt(3) term in the formula.

You cannot mix line current and phase voltage in calculating watts (or VA).
 
GoldDigger said:
We are assuming that this is a 240V delta, so the voltage to neutral is 139V. And 139V x 20A x 3 = 240 x 20A x sqrt(3).

That is another simple way of deriving the sqrt(3) term in the formula.

You cannot mix line current and phase voltage in calculating watts (or VA).
Click to expand...
??
240 3ph wye (3P4W), where does 139v come from? Ph-N is 240v
sorry, i meant Y. but even with "3P4W 240v Open Delta" or the "3P3W 240 Delta", the ph-ph is 240v, and wild leg to N (B-N) is 208 while AC to N (A-N and C-N) is 120v.
415V-Wiring-Diagram-3-Phase-4-Wire.png
 
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but even in 240 delta, 20A per leg is still ~2.5kW over rated HP, if PF=0.9 under load assumably.
 
FionaZuppa said:
??
240 3ph wye (3P4W), where does 139v come from? Ph-N is 240v
sorry, i meant Y. but even with "3P4W 240v Open Delta" or the "3P3W 240 Delta", the ph-ph is 240v, and wild leg to N (B-N) is 208 while AC to N (A-N and C-N) is 120v.
415V-Wiring-Diagram-3-Phase-4-Wire.png
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IF the supply is 240 wye you need to specify that clearly, as it is relatively uncommon. For 240 wye you would NOT generally use a motor nominally rated at 240V since the motor rating almost always specifies the line to line (across winding) voltage. But, yes there can be motors wound for 240 wye.

You are correct that when 240 is the wye voltage the power calculation uses a full factor of 3.

If you are using the line to line voltage, you need to match it with the line to line current, which is NOT equal to the individual line current. That is where the factor of sqrt(3) comes in then.
 
Fair enough. Can we see a pic of the motor spec plate.
 
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