240V mains blown fuse indicator - Questions

Thread Starter

WillL84

Joined Jan 4, 2023
16
I need to wire up a panel with 10 separate 240V receptacles. These will be used for heaters in an industrial application. I also need to install blown fuse indicators in the box. My question is will I need to make 20 of them (one for each 240V line) or only 10 (one per pair)? MY thinking is I'll need 20 as if only one fuse pops the indicator will only light up on the popped one. But will this not matter since it's AC? Also what if both fuses pop?

We use terminal block fuse holders with indicators, just a simple 100k resistor with an LED. But that will only light if that fuse goes. If the other fuse goes will it still light? If both fuses blow will it still light? Thanks in advance.
 

SamR

Joined Mar 19, 2019
5,078
Welcome to AAC!

Typically, for questions like this, consulting your local electrical code regulations is the answer. Here in the US that is the National Electrical Code (NEC) part of the National Fire Protection Association (NFPA) US Fire Code, the answer here is YES, both legs must be fused. Local codes may have more stringent regulations than national or regional codes. You need to know which is the ruling body for your location and consult their regulations.
 

Thread Starter

WillL84

Joined Jan 4, 2023
16
I'm familiar with the code and I know both legs must be fused, I'm just wondering how the blown fuse indicator will work if the fuse blows that the indicator is not attached to or if both fuses blow
 

MisterBill2

Joined Jan 23, 2018
19,424
Use neon's, then both should light for sure. if both fuses blow.
Max has it right!! Use neon indicators across each fuse, if both fuses pop then each indicator will have 120 volts. IIf the indicators can be in the same panel as the fuses the wiring will not be much. The only issue is that they are not as bright as regular indicator lights. You can probably use transformer type 120 volt incandescent pilot lights but that would cost a lot more.
 

Thread Starter

WillL84

Joined Jan 4, 2023
16
Ok so when these heaters fail sometimes it takes out only one fuse, other times both. So what I'm wondering is if I need to hook up 20 indicators (one for each line for 10 plugs) or if I can have just one indicator that will light if either fuse blows or both fuses blow.
 

crutschow

Joined Mar 14, 2008
34,842
Likewise if I have an indicator on each leg and BOTH fuses blow then neither will light as there will be no return path, correct?
No.
The return path is through the load and each indicator, which would all be in series.
Makes little difference whether one fuse blows or both blow.
 

Thread Starter

WillL84

Joined Jan 4, 2023
16
In such case return path will through load.
If both lines are disconnected from the load there will be no return path. If only one fuse blows then there will still be a return path through the other fuse.

I almost need to make a PCB with logic gates like this:
Untitled.png

That way if either or both fuses blow the output to the indicator will be high.

Then again because these are heater cartridges the power won't be constant, it'll only be on when the controller PWMs the heater. So the indicator will start blinking in accordance to the controller calling for heat. Which isn't the end of the world I suppose.
 

Externet

Joined Nov 29, 2005
2,247
need to install blown fuse indicators
If breakers instead of fuses, red indicates tripped. Do you really need to be lit ?:
1672865957819.png

For fuses, see post # 6

Main breakers are joined. Any trips, the other also disconnects, and red flag always shows for models featuring the indicator :
1672866494506.png
1672866862190.png
 
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Thread Starter

WillL84

Joined Jan 4, 2023
16
If breakers instead of fuses, red indicates tripped. Do you really need to be lit ?:
View attachment 284467

For fuses, see post # 6

Main breakers are joined. Any trips, the other also disconnects, and red flag always shows for models featuring the indicator :
View attachment 284469
View attachment 284470
Yes we need indicators at the outside of the panel so we can see if a heater failed.

I buy fuse holders with indicators already on them.
We have those already but they're useless when the indicator is inside the enclosure. This is one piece that will have ten separate heating elements in it (all controlled by one temperature controller) and we need to know if one element fails as that will cause the heating to be uneven and can affect the extrusion.
 

Danko

Joined Nov 22, 2017
1,857
We have those already but they're useless when the indicator is inside the enclosure. This is one piece that will have ten separate heating elements in it (all controlled by one temperature controller) and we need to know if one element fails as that will cause the heating to be uneven and can affect the extrusion.
What is power of one heating element?
 
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