Disconnect

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Brandon Lynch

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Not sure if this is the right area so please excuse me if it is not....
Talking with one of our electrical engineers and he is under the assumption you can mount a 60 amp fused Disco. Use one leg 30amp fused for heaters and the other leg fused at 15amp for control panel power. One neutral #10 to feed both, if he shares a neutral at the least (at the least) thats 45 on #10... 10 is good for 30 and 12 is good for 20. I am tired of discussing it and can not find any definition in the code book on proper disconnect usage.... This is not for HVAC or pool/spa
 
This sounds to me like a multi-wire branch circuit, as is allowed by NEC article 210.4 I don't quite understand what you mean by, "that's 45 on a #10." But it is OK to put fuses in a disconnect switch that have a lower rating than that of the disconnect itself. I don't know of a reason you can't use a two-pole disconnect to serve two different loads, using different fuse ratings. I also think it is OK to share a neutral, if you meet the requirements of 210.4. Those requirements include that both sources must come from the same panelboard, and that the act of opening one leg must also open the other leg. Finally, you need size the neutral for the maximum unbalanced load, which would be the 30 amps. So a #10 neutral looks right to me.

Is there a particular reason you don't think that this installation would be legal under the NEC?

Welcome to the forum.
 
If you have 30 amps fused on one leg and 15 amps fused on the other leg then the neutral only carries the difference between 30 and 15. 30-15= 15 amps on the neutral assuming single phase. Not 30 + 15
 
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Dasiy chaining the 30amp fuse and 15amp fuse line side.... Is a question I have. I maybe looking at this all wrong. But the Disco started out as 30amp fused now they are wanting to add a 15amp fuse using the 30amp line side coming in? The 30amp was supposed to handel 1 1000w heater and 2 750w heaters and the 15amp for the control panel... If by chance the 15 maxes and the 30 maxes thats 45amps on a #10... Sorry guys
 
Look at a single pole 30A breaker. You can use that to feed any size fuse you want.
If the fuse size is less than 30A it may blow before the breaker trips.
If the fuse is larger than 30A it may not blow before the breaker trips.
The only difference with a two pole breaker is that when one pole trips it will open both poles while a fuse will open only one pole.

Tapatalk!
 
GoldDigger said:
Look at a single pole 30A breaker. You can use that to feed any size fuse you want.
If the fuse size is less than 30A it may blow before the breaker trips.
If the fuse is larger than 30A it may not blow before the breaker trips.
The only difference with a two pole breaker is that when one pole trips it will open both poles while a fuse will open only one pole.
Tapatalk!
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If you are worried about putting a 15 and a 30 amp fuse in parallel on the same breaker pole, then it us possible that the breaker will not be able to hold with both loads on. But that depends on the load current, not the fuse size.
It is common to have the total of the breakers on one phase in a panel be greater than the size of the main

Tapatalk!
 
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I think we need to know, are you utilizing both legs for the heaters (240 volts) or are you running them off only one of the fuses? You also made a comment on taking 15amp off the line side is this what you meant to say if so you can't double wires up in the line side lugs to run out to another 15 amp fuse. And why or what is this control panel supposed to do can you just use line voltage thermostats on the heaters?
 
As noted, we may need some clarification.
If you have (1) 30 amp single pole breaker &#10 neutral supplying the disconnect
and that ONE @10 is feeding a 30 amp and 15 amp fuse, depending on the loads, it may be a problem, however, the 30 amp breaker will protect the circuit.
If it fed with a 2 pole breaker, two phases and a neutral, the shared neutral will only carry the unbalanced current.
 
Edited because I didn't see the shared neutral statement, ok you have basically two 120 volt loads the heaters and the control panel, the heaters @ 2500 watts will pull 20.8 amps, the control will depend upon how many relay coils and other controls are in it but I suspect will be a very low load, as long as the neutral is sized for the largest load (heaters) and each load is on a different leg so that you will have 240 volts between each fuse or leg in the disconnect then you basically have a multi-wire circuit and the neutral will only see the differential current even if the heaters short so they pull 30 amps, and the controls pulls 15 amps the neutral will only see 15 amps, you do not add the two together, if the disco is fed from the same phase or leg then as you say the neutral will see the sum of both circuits.

If as I calculated the heaters pull 20.8 amps and you have 10 amps of control current then the neutral will only see 10.8 amps.

Even if the imbalance was to go totally to the heaters then the neutral would still only see the 20.8 amps as a max
 
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