Breaker Didn’t Trip When Heater Wire Shorted to Ground on Blow Molding Machine—Why?

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Why the breaker and fuses did not trip on ground fault
#1 21682020 28 Feb 2019 21:19

Travis Rudloff Travis Rudloff

Anonymous

Why the breaker and fuses did not trip on ground fault
Post #1 21682020 28 Feb 2019 21:19

I have a set of heating bulbs on a blow molding machine. Heaters are 240 and wiring starts through fuses and then through a motor protector breaker/contactor and then a PLC and then through a relay before it gets out to the heaters themselves. (weird manufacturer setup). One of the wires in the 24 conductor cable went short to ground and fried the PLC and the relay but the breaker on the motor protector never tripped and it never blew any fuses. Just wondering why it did not trip the breaker.
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Clarifying cable, relay, and PLC damage details
#2 21682021 01 Mar 2019 01:26

Rick Curl Rick Curl

Anonymous

Clarifying cable, relay, and PLC damage details
Post #2 21682021 01 Mar 2019 01:26

Hi Travis-The thing in your description that jumps out at me is that a 24 conductor cable is involved. It is unusual to have high voltages and currents in a 24 conductor cable. Is this the cable feeding power to the heating bulbs or is it a low voltage control cable? What part of the relay was fried- coil or contacts? What is damaged on the PLC- just one output or more than one? Is the PLC switching 240 directly or is it at a lower voltage?I can probably help with the answer after you give me a little more to go on.-Rick
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#3 21682022 01 Mar 2019 01:33

Travis Rudloff Travis Rudloff

Anonymous

Post #3
21682022 01 Mar 2019 01:33

The cable is supplying power to the bulbs through a 24 pin plug. Not sure which part of relay went bad, it actually caught fire. The PLC has 2 banks on it. The top bank has 4 signals coming out that are not working. The bottom 4 signals are working though. PLC is switching 240 directly. The setup confuses me because I've never seen so many components just controlling heaters.
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Clarifies 120 V PLC wiring and Crouzet relay setup
#4 21682023 01 Mar 2019 02:54

Travis Rudloff Travis Rudloff

Anonymous

Clarifies 120 V PLC wiring and Crouzet relay setup
Post #4 21682023 01 Mar 2019 02:54

Rick I lied to you. The PLC input and output voltage is 120. From the contactor behind the breaker they split the voltage. They run connections in series from one side of the contactor to the PLC and then up to the 120v Coil on the relays. And then they run out the other side of the contactor in full 240 to the other side of the relay. The relay is a little strange. Made by Crouzet, XTRIR3 if that helps you with anything. I'm fairly new to electrical system troubleshooting so it's a learning curve for me.
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#5 21682024 04 Mar 2019 20:56

Rick Curl Rick Curl

Anonymous

Post #5
21682024 04 Mar 2019 20:56

Hi Travis-So far I have not been able to find the specs on the XTRIR3 relay.What was it that failed? Is it just one output of the PLC? On the relay- is the failure on the coil side or the contact side? Are you sure the power to the PLC and the relays is going through the same motor protector that feeds the heating bulbs?-Rick
#6 21682025 05 Mar 2019 19:20

Travis Rudloff Travis Rudloff

Anonymous

Post #6
21682025 05 Mar 2019 19:20

On the relay the coil fried.I lost 4 output's on the PLC.Yes, behind the motor protector is a contactor and I have 120 out of one side of the contact and . 240 out the other. It's split somewhere. The 240 goes to contacts on the relay and the 120 goes through the plc and then up to the coil on the relay.
#7 21682026 29 Mar 2019 10:42

francis gyuhui francis gyuhui

Anonymous

Post #7
21682026 29 Mar 2019 10:42

Is this the cable feeding power to the heating bulbs or is it a low voltage control cable? What part of the relay was fried- coil or contacts? What is damaged on the PLC- just one output or more than one?
#8 21682027 30 Mar 2019 09:58

francis gyuhui francis gyuhui

Anonymous

Post #8
21682027 30 Mar 2019 09:58

Is this the cable feeding power to the heating bulbs or is it a low voltage control cable ? What part of the relay was fried- coil or contacts? What is damaged on the PLC- just one output or more than one?
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Topic summary

A blow molding machine's heater circuit includes 240V heating bulbs powered through fuses, a motor protector breaker/contactor, a PLC, and a relay. A 24-conductor cable supplies power to the heaters via a 24-pin plug. A short to ground on one wire caused the relay coil to catch fire and damaged four outputs on the PLC, but the motor protector breaker and fuses did not trip. The PLC operates at 120V on inputs and outputs, with the 240V supply split at the contactor: 120V feeds the PLC and relay coil, while 240V feeds the relay contacts and heaters. The relay involved is a Crouzet XTRIR3. The failure likely occurred on the relay coil side. The unusual wiring setup and voltage splitting may explain why the breaker did not trip during the short circuit.
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Breaker Didn’t Trip When Heater Wire Shorted to Ground on Blow Molding Machine—Why?

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Topic summary