switch from fuses to circuit breaker machine heat circuit

[lew5679]

I have heat circuit 460 volt with 5 heaters. the heaters are 2 wire. so one leg is connected to one side of 3 heaters the other leg is connected to one side of the other 2 heaters and the last leg is connected to the other side of all 5 heaters. each leg has a different amp fuse 25A 20A and 30A . I would like to switch this circuit over to a breaker instead of fuses. should i put in 3 different size breakers or would a 30A 3 pole breaker work. the wire size is all the same on the entire circuit.

 

[LarryFine]

Welcome to the forum.

Can you rewire the heaters so they're more balanced? I.e., two, two, and one.

 

[lew5679]

Welcome to the forum.

Can you rewire the heaters so they're more balanced? I.e., two, two, and one.

I cant do that . the heater bands are 2 wire and the 460 supply is 3 wire
i cant see where to attach a picture of the print from my computer

 

[ptonsparky]

PHASE:
AB
BC
CA
AB
BC

 

[lew5679]

i could do that
my heaters are 460volt 3000w
what fuses or circuit breaker should i use if i wire it that way
the heats are wired with 10 gauge wire

 

[lew5679]

PHASE:
AB
BC
CA
AB
BC

i could do that
my heaters are 460volt 3000w
what fuses or circuit breaker should i use if i wire it that way
the heats are wired with 10 gauge wire

 

[ptonsparky]

i could do that
my heaters are 460volt 3000w
what fuses or circuit breaker should i use if i wire it that way
the heats are wired with 10 gauge wire

Quick guess. 2 - 3 pole 20 amp would work

 

[LarryFine]

The heaters use about 6.5a each.

I cant do that . the heater bands are 2 wire and the 460 supply is 3 wire'

Move one heater of the three to be between the to lines that presently have no heater between them.

i cant see where to attach a picture of the print from my computer

In the bar atop the response window, click on the little frame with the sun and mountains; then click in the box that says Drop Here.

 

[lew5679]

thanks here is the print for one heat zone

 

[lew5679]

The heaters use about 6.5a each.


Move one heater of the three to be between the to lines that presently have no heater between them.


In the bar atop the response window, click on the little frame with the sun and mountains; then click in the box that says Drop Here.

 

[ptonsparky]

Why do you want to reinvent the wheel here? You have the original schematic.

 

[lew5679]

Why do you want to reinvent the wheel here? You have the original schematic.

we seem to blow a lot of fuses during heat up even after checking all heater bands and connections and the fuse holders get hot and have failed themselves. also when some of people diagnose a problem they go through several fuses and they are not cheep anymore so i would like to switch to circuit breakers i was hoping to put a 3 pole breaker in the circuit instead for safety reasons also

 

[ptonsparky]

Remove my suggestion from your thoughts. It's not the proper solution.

 

[jim dungar]

You have two sets of resistors in parallel. Your equivalent resistance, for the three heaters is about 23.8 ohms so the current through the 25A fuse could be near 21A so would not be surprising to find it 'runs hot'.

 

[petersonra]

It looks to me like it was done this way to save on solid state relays.

I don't see why you couldn't replace the three single fuses with three single circuit breakers of the same rating if all you want to do is be able to reset the circuit breakers instead of replacing fuses.

Personally I think I would look a little closer at why the fuses are blowing in the first place.

 

[ptonsparky]

IDK how the SSRs are controlled but I see at least three different levels of heat.

What is the actual applied voltage?

 

[lew5679]

IDK how the SSRs are controlled but I see at least three different levels of heat.

What is the actual applied voltage?

the SSRs are controlled by a plc heat setting and a thermocouple so we can set the heat to whatever temp we want. the applied voltage is 460v

 

[lew5679]

It looks to me like it was done this way to save on solid state relays.

I don't see why you couldn't replace the three single fuses with three single circuit breakers of the same rating if all you want to do is be able to reset the circuit breakers instead of replacing fuses.

Personally I think I would look a little closer at why the fuses are blowing in the first place.

i have looked into single circuit breakers but i have not been able to find a 30A 480v single breaker
I believe the fuses are blowing because they are so close to what the heats draw for amperage, then you need to include all the connections fuse holder wire length and during initial start up the heats are on constant for 1 hour or so this is when we are having the issue once up to heat we don't ever blow fuses there are 9 heat zones on each machine so there are 27 fuses 9 three fuse holders mounted on a din rail stacked up against each other creating a lot of heat

 

[petersonra]

Have you considered installing a stirring fan to blow some air on the fuses? Might just be bad ventilation inside the control panel.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

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Is there room on the din rail where the fuses are located to separate them a little. Even a small separation will do wonders for the temperature there.

 

[ptonsparky]

Have you considered installing a stirring fan to blow some air on the fuses? Might just be bad ventilation inside the control panel.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Is there room on the din rail where the fuses are located to separate them a little. Even a small separation will do wonders for the temperature there.

I was going to post a picture of a house we were in that had a fan blowing on the panel. Totally open with no door.
(Can't find it.)