Electric Heater Fusing

I typically design a heater circuit like this:

3 phase fuse block -> Shutoff Contactor -> 2 or 3 phase SSR-> Heater Bundle (Delta Wired)

However, I have a heater that is unexpectedly going to have two bundles of heaters inside to make its rated kW, with 6 terminals to wire to instead of 3. Can I jumper the terminals inside of the heater for parallel power wiring of each bundle? Obviously the wire feeding the heaters will be sized appropriately. Or does code require that I protect each bundle individually with fuses?

Thanks!

If you reduce the wire size to half, the length of it should be according to code.The code does not require overcurrent(for heaters that is), however it does need shortcircuit safety.

Thanks for the response- so basically I just need to protect the wires feeding it, and not the device itself like a motor would require?

I think it should not be a problem to connect them in parallel, but have you looked if there is any difference in price to go 2x50%. This way you could easily deactivate one element bundle if it we're damaged. Or run on one element when there is no need for heat.

2 bundles of heaters each with 3 wires
Each bundle of heaters must be wires separately and fused separately
There is a UL code covering paralleling feed wires outside a panel.
They must be above a certain size I believe It's above 4/0 then you can use a single fuse for the wires on each phase.

if i understand you correctly,

from the control panel
a. 3 phase fusing for the wire to the contactor / ssr control
rated for the load
b. 3 phase fusing to protect the wiring to both heaters
at the heater connection panel.
c. power distribution block to separate the heaters
d. (2) 3 phase fuse blocks - 1 for each heater

the only problem i see is detecting when one of the heater elements goes bad.

just my 2 cents.

regards,
james

I don't see the problem
you can monitor the current on each heater element or you can monitor the current on the feeder at the contactor either way will work as well.
a large imbalance is what you are looking for.

GaryS,

the reason i mentioned it is because of a job i did for a company.
the process required so many kw of heat for a specified time.
we had load monitors on the heater (1 heater per unit).

james

I'd personally go with individual fuses per heating unit (bundle). Very fast and easy to troubleshoot which one is shorted via checking voltage across fuse. However, it won't tell you too much if an individual element is open without checking current.

I've had some experience troubleshooting element banks consisting of over a hundred individual elements that are wired in a combination series parallel configuration up at the element terminals which is not a very convenient location for disassembling and doing resistance checks to see which ones are failing, but doing a quick voltage across fuse test beats clamping individual wires and comparing values against a benchmark while running 100% output.