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Old 12-10-2019, 12:23 PM   #41
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Originally Posted by macmikeman View Post
Wirenutting nailed this. The repeated bogging down of the load is probably the answer. I recently was amp checking a box manufacturing operation for a moving company. They build big hauling boxes onsite for moving furniture and the like and are pretty much one time use so these guys build seventy or eighty big boxes a day. The table saws were tripping often, not a voltage drop problem. It turned out to be the operators- they would bog the saw blades during ripping plywood sheets constantly. Blades would stop. #10 wires were melting. Sometimes the breakers didn't trip till stuff started smoking. Would not have mattered if I ran #6 to the saws, the operators are the problem. They are under pressure to hurry all the time. Very hard to communicate to them, they are all from an island chain out there where there are French Electricians and no speaky Englisky.
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Old 12-10-2019, 02:58 PM   #42
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Default SqD Heater Elements Sz3

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This control panel has fuses, and yes the fuses went out. The wire was defintely undersized, but I just thought the insulation would handle at least 60A before melting. I think the OL's should have tripped at about 52-56

SQ D 87.7 I think they were

NEMA heater tables already include the service factor of 1.15 for 1.15 service factor motors, you are supposed to size them for the motor nameplate value or deduct 15% for 1.0 service factor motors.


Table for a Size 3 starter, using CC type overloads, remember that the table values show nameplate values, but give you another 15% as standard.


CC87.7 ultimate trip point is 61.41 with the 15% included.



Thhn Insulation Melting-sz3-sqd-heaters.jpg
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Old 12-10-2019, 08:40 PM   #43
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Are the heater elements those bimetallic style that start with a B---?

What is the part number for the heater elements?

I've seen A LOT of starters over the years with the overloads sized/set to 125% of the motor nameplate, even though they should be sized to 100% of the nameplate since they are set to trip at 125%. Nobody usually notices the error until later, when something burns up. Sometimes years down the road.

It sounds as though this machine has the potential to be overloaded by operator input fairly easy, so it's definitely worth verifying it's correct in my opinion.


EDIT: A CC87.7 bimetallic looks like it could be 1-3 sizes over the size it should be for a 46 amp nameplate motor depending on which column you should be using on this chart:

https://www.google.com/url?sa=t&rct=...f9kR3YbtDMffQL

Take a look at the bottom of this pdf. It mentions how to do some of the sizing for Sq D's overloads.
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Originally Posted by CMP View Post
NEMA heater tables already include the service factor of 1.15 for 1.15 service factor motors, you are supposed to size them for the motor nameplate value or deduct 15% for 1.0 service factor motors.


Table for a Size 3 starter, using CC type overloads, remember that the table values show nameplate values, but give you another 15% as standard.


CC87.7 ultimate trip point is 61.41 with the 15% included.



Attachment 138752
Thanks, I didn't know that you are supposed to use the nameplate value without adding 125%. I didn't have time today to look again at those heaters, and verify the number. Do recall 87.5 I thought, but the chart looks like it's 87.7 I thought the boss said it should be protected at 52A and that it was right. Definitley looks oversized on the chart above
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Old 12-11-2019, 03:06 PM   #44
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Cc 81.5
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Old 12-11-2019, 03:48 PM   #45
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For your future knowledge, read the sizing information, at the bottom of the charts, in the link given previously. It's good info to keep in your knowledge base, for all NEMA starters.
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Old 12-11-2019, 10:01 PM   #46
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My guess would be some combination of problems to cause the wire to melt.
Possibilities:
Overloads oversized
Overloads bypassed
Excessive loading of the motor
Previously damaged insulation allowing a high resistance fault to the raceway
Mechanical problem(s) with motor or machine
Motor starting under high load repeatedly
Ground fault on ungrounded system

There are always other odd things that no one thinks of to cause you grief.

There is never a dull day fixing old dilapidated industrial equipment. Some of the junk, that I repair, should have been thrown away years ago.
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Old 12-12-2019, 12:15 AM   #47
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Any chance of a chemical attack? Like cleaning solution or something along those lines?
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Old 12-12-2019, 11:15 AM   #48
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Anyone up for an experiment?
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Old 12-12-2019, 02:02 PM   #49
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I do know from experience from when I was young and dumb that #10 THHN will melt almost right away and fill a pickup truck cab with smoke if shorted across a car battery with no fuse. I had a set of fog lights I hooked up too the wrong side of a fuse block, the wire went thru the firewall and shorted to it from rubbing. I had two girls in the front seat when it shorted and the truck filled with smoke and stopped running, you should of heard them screaming FIRE. Me I reached down and ripped the wire out, burnt my hand it was so hot, all in about 15 seconds.
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Old 12-12-2019, 04:14 PM   #50
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I do know from experience from when I was young and dumb that #10 THHN will melt almost right away and fill a pickup truck cab with smoke if shorted across a car battery with no fuse. I had a set of fog lights I hooked up too the wrong side of a fuse block, the wire went thru the firewall and shorted to it from rubbing. I had two girls in the front seat when it shorted and the truck filled with smoke and stopped running, you should of heard them screaming FIRE. Me I reached down and ripped the wire out, burnt my hand it was so hot, all in about 15 seconds.
Two girls? That’s greedy. You don’t believe in sharing?
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Old 04-15-2020, 11:01 AM   #51
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I do know from experience from when I was young and dumb that #10 THHN will melt almost right away and fill a pickup truck cab with smoke if shorted across a car battery with no fuse.

Could have been a couple hundred amps on that wire. Current basically limited by the resistance of the short to the body.
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Old 04-15-2020, 01:24 PM   #52
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The Ol's were sized properly, but didn't trip ??? wth ?
Thermal OLs are crap tested many and had many fail.
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Old 04-15-2020, 07:25 PM   #53
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99% of the time ive seen the wires melt together in a non metallic flex it due to a overheated ground wire. Got to love working with welders.
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Old 04-15-2020, 08:32 PM   #54
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I think I read every post and didn’t see one response questioning the distance or possible voltage drop.
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Old 04-15-2020, 09:04 PM   #55
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How long of a run to the motor? Possibly a voltage drop problem?


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Old 04-18-2020, 04:46 PM   #56
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I think I read every post and didn’t see one response questioning the distance or possible voltage drop.


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How long of a run to the motor? Possibly a voltage drop problem?


Nah on the voltage drop, 480V 40hp #6 tray cable I recall, at maybe 100'

The grinding wheel has a long lever with lots of leverage, that the operator uses to apply pressure to grind the ingot. I watched him, and there is an amp meter for him to watch what he's doing.
I think some of these guys on another shift just lean on that thing, and almost lock the rotor.
Once I replaced the 8 with 6, no issues since.

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