4 pole disconnect 80 or 100 amp

[palmtreeguru]

Is there such an animal as a 4 pole 80 or 100 amp disconnect? Trying to get connect a tankless electric water heater that is 36kw and the terminal block has 4 lugs that are connected internally so the circuit would be parallel. I know the NEC code allows a parallel circuit with 1/0 wire, however we still want to avoid the chance of any back feeding if one of the two 80 amp double pole breakers is not switched off. Is there a 4 pole disconnect out there rated for that amperage? Thanks

 

[jim dungar]

Yes. Most disconnect/safety switch manufacturers offer a 4 pole non-fused version, but they are likely limited to the 600V heavy duty styles.

 

[palmtreeguru]

Thank you

 

[texie]

Is there such an animal as a 4 pole 80 or 100 amp disconnect? Trying to get connect a tankless electric water heater that is 36kw and the terminal block has 4 lugs that are connected internally so the circuit would be parallel. I know the NEC code allows a parallel circuit with 1/0 wire, however we still want to avoid the chance of any back feeding if one of the two 80 amp double pole breakers is not switched off. Is there a 4 pole disconnect out there rated for that amperage? Thanks

The wording of your post seems to imply that the 2 feeds are in parallel. This is not safe or allowed. Can you give more details?
Units like this are normally designed for 2 branch circuits.

 

[palmtreeguru]

You are correct, that is the case it would be in parallel so if we ran the two double pole 80's into a 4 pole disconnect then ran the power from that to the heater would that resolve the problem because now when you kill the power at the disconnect it is off at the heater?

 

[hillbilly1]

They are not in parallel, they use triacs to control the separate heating elements, each input is isolated. Control power is pulled off only one two pole input, if that input is not live, the WH will not work.

 

[texie]

You are correct, that is the case it would be in parallel so if we ran the two double pole 80's into a 4 pole disconnect then ran the power from that to the heater would that resolve the problem because now when you kill the power at the disconnect it is off at the heater?

No, this is not allowed. The circuits can't be connected together in the heater. Is this a listed product?

 

[synchro]

Are you sure that the water heater loads are internally connected in parallel?
For example the Rheem 36 kW specifies the use of four separate circuits with each having a 40A 2-pole breaker and using 8 gauge wire.

https://s3.amazonaws.com/WebPartners/ProductDocuments/1F902225-3EB3-4E61-A537-4D577FB7272C.pdf

 

[hillbilly1]

Sorry, I said triacs, but they are actually SCR’s! Just remembered! Sux getting old!

 

[synchro]

Sorry, I said triacs, but they are actually SCR’s! Just remembered! Sux getting old!

Actually, I believe you were right in the first place. Triacs are needed for switching AC because they conduct current in both directions, while SCRs are unidirectional. Triacs are very similar to having two SCRs connected in parallel but reversed in polarity (anti-parallel) so that it can conduct current in both directions.
SCRs, Triacs, GTOs, etc. are all different types within a broader category called thyristors. But they all rely on the basic SCR principle and so often they are just called SCRs.
By the way, an SCR is really a PNP and an NPN transistor connected with positive feedback. So after you trigger it with a small input the current will increase quickly and it will "latch" ON. Then it will stay ON until the source of current disappears.