CaliforniaMike
Member
Hello,
I generally work on small stuff and just got pulled into evaluating a prototype production tool that that the electricians have been having problems with. Suggestions, or even rants, re general safety as well as NFPA and NEC regs would be appreciated.
We are designing some mobile heater control panels for for use in production with some presses. Local power in the press is 480VAC single phase. The heating control panels will be running at 240VAC. We are planning to feed 480 to a switched plug on the side of the press cabinet, through a cable with a plug, to the portable heating panel.
We are mounting a dry type transformer to the outside of the heating control panel and running leads through conduit to the cabinet with the heating panel.
Transformer is rated for 10 kVA. Overcurrent coordination on this TX is a challenge since the manufacturer has now volunteered that they design for a inrush currents of ~30 x FLA. We consistently blow 15X @ single cycle rated fuses on prototypes so this is real. This was where I got pulled in.
Initial design was to bring 480 into cabinet and land it on a fusible disconnect and then feed the step down TX. With a need to handle a 30X inrush, we now know that there are no fuses (CC style) that will fit the disconnect and survive the inrush, even at a 250% rating.
We have a space issue in the heating panel, but some room in the press panel. Actual expected load is well under the 10 KVA and TX is fused at the output at 35A.
The plugs that we would like to use are rated to 20 Amps. We are looking at using IDSR 20A fuses to protect the plug on the press cabinet. These would in turn be fed by the fusible disconnect in the press control panel cabinet. The IDSRs have great inrush tolerance and will allow us to fuse at 20 to use the smaller plugs, sockets, and cord while still withstanding the inrush into the TX in the heating panel. If we go this route, we are coordinated for overcurrent up to and including the panel breaker.
Two questions:
1) Is 30 x FLA normal? I have always designed to 15 x FLA and was a bit surprised to find that this was the problem.
2) Do we need to have input protection to the TX in the heating control cabinet if the power from the press panel is already protected at less than the FLA rating of the TX?
3) If 2 is acceptable, we would land power to the heating cabinet on the disconnect. However, we now have several of the heating panels built up and there are no fuses available for the fusible disconnect that will withstand the inrush to the TX. Since the disconnect is protected upstream at 20A, can we bypass the fuse clips in the disconnect and use it only as a disconnect? (Yes, a "penny" in the fuse box ...)
I have never done either of these (2,3), but we are in make it work mode and with the 20 A fuse up circuit, they seem to address all overcurrent and disconnect issues.
Thanks,
Mike.
I generally work on small stuff and just got pulled into evaluating a prototype production tool that that the electricians have been having problems with. Suggestions, or even rants, re general safety as well as NFPA and NEC regs would be appreciated.
We are designing some mobile heater control panels for for use in production with some presses. Local power in the press is 480VAC single phase. The heating control panels will be running at 240VAC. We are planning to feed 480 to a switched plug on the side of the press cabinet, through a cable with a plug, to the portable heating panel.
We are mounting a dry type transformer to the outside of the heating control panel and running leads through conduit to the cabinet with the heating panel.
Transformer is rated for 10 kVA. Overcurrent coordination on this TX is a challenge since the manufacturer has now volunteered that they design for a inrush currents of ~30 x FLA. We consistently blow 15X @ single cycle rated fuses on prototypes so this is real. This was where I got pulled in.
Initial design was to bring 480 into cabinet and land it on a fusible disconnect and then feed the step down TX. With a need to handle a 30X inrush, we now know that there are no fuses (CC style) that will fit the disconnect and survive the inrush, even at a 250% rating.
We have a space issue in the heating panel, but some room in the press panel. Actual expected load is well under the 10 KVA and TX is fused at the output at 35A.
The plugs that we would like to use are rated to 20 Amps. We are looking at using IDSR 20A fuses to protect the plug on the press cabinet. These would in turn be fed by the fusible disconnect in the press control panel cabinet. The IDSRs have great inrush tolerance and will allow us to fuse at 20 to use the smaller plugs, sockets, and cord while still withstanding the inrush into the TX in the heating panel. If we go this route, we are coordinated for overcurrent up to and including the panel breaker.
Two questions:
1) Is 30 x FLA normal? I have always designed to 15 x FLA and was a bit surprised to find that this was the problem.
2) Do we need to have input protection to the TX in the heating control cabinet if the power from the press panel is already protected at less than the FLA rating of the TX?
3) If 2 is acceptable, we would land power to the heating cabinet on the disconnect. However, we now have several of the heating panels built up and there are no fuses available for the fusible disconnect that will withstand the inrush to the TX. Since the disconnect is protected upstream at 20A, can we bypass the fuse clips in the disconnect and use it only as a disconnect? (Yes, a "penny" in the fuse box ...)
I have never done either of these (2,3), but we are in make it work mode and with the 20 A fuse up circuit, they seem to address all overcurrent and disconnect issues.
Thanks,
Mike.
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