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measure single phase 240v motor

a motor has been tripping out the breaker. (single phase 240v) If i disconnect the motor from the contactor the breaker stays latched the contactors also latch in indicating a fault on the motor.

How can I be sure that the motor is faulty?. the motor has a capacitor on the top so i assume it's a capacitor start/run motor.

The only wires going from the contactors to the motor are LIVE, NEUTRAL, EARTH

If i put a meter across the live and neutral I get 2000 ohms which sounds very high to me. There dosen't seem to be any leakage from the live or neutral down to earth.

am i reading this right?

Reply to
Ronbol
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Not as I understand your post. 240v is 2 hots, not as you described "LIVE, NEUTRAL, EARTH" A neutral or grounded conductor would have no business in a 240v motor, not any I have seen.

Guessing your wiring is wrong inside the motor.

I do not have a clue why you would ohm the hot and neutral in this situation.

Reply to
SQLit

It might help if you post the name of the country you are in - otherwise you might confuse a few people.

The type of earth bonding your supply has may help too..

Reply to
Palindr☻me

If there where two hots and earth where would you ohmm?

Reply to
Ronbol

I assume you are measuring the resistance at the motor terminals with the power off, right?

  1. Was the motor working before?
  2. Does the motor try to start or it just sits there humming a few seconds before the breaker trips?
  3. Have you tried to wire the motor to an other breaker? Observed any difference? If the answer is yes to 3., then I would check the starting capacitor and the centrifugal switch in the motor if there is one. Gene
Reply to
EpsilonRho

yes

has been yes

breaker trips straight away

breaker and motor contactor hold in without motor connected.

Reply to
Ronbol

UK supply, not sure on the earth bonding

Reply to
Ronbol

Before you begin to do anything with the motor, make sure that the breaker is not at fault. Replace the breaker temporarily with an other one with the same amperage. If it happens again, then the motor is the culprit. Testing the breaker without load is quite meaningless.

If it is the motor then we must exclude miswiring because you said it worked before. So what could it be?:

  1. Motor mechanically frozen. Does the shaft rotate freely?
  2. Any shorts inside the motor contactor?
  3. Starting capacitor shorted ---> Replace and test
  4. Winding shorted ----> buy a new motor or have it rewound if it is worth it.

Gene

Reply to
EpsilonRho

In England a single phase 240v motor would not work without a neutral.

So Its probably wired correctly.

The reason you would ohm the Live & Neutral would be to see if there was a short on the motor.

sQuick..

Reply to
sQuick

What are you using to measure the resistance?

If its just a normal multimeter a fault might not show up.

Really needs to be tested with an Insulation Resistance Tester.

sQuick..

Reply to
sQuick

OK so, between live and neutral still sounds high, does it to you.

Reply to
Ronbol

I agree. You should be using a Megger. What is the FLA of the motor, and what is your breaker size?

Reply to
engineer

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