I am attempting to explain to a licensed electrician why an onstage switch would need to be fused.
In our example, there is a 100A 3-phase (4 wire + ground) feed to the stage, which is directly wired from a 100A 3-pole breaker in a separate panel. That panel is in another room.
The box they have installed (which I am questioning) is a simple safety switch with no internal fusing. For budgetary reasons, the client needed to go this route instead of installing a pre-manufactured theatrical company switch, which would of course have its own breakers. The switch is located onstage where it would only be operable by qualified personnel. It is likely that the first uses of this power source will use temporary Cam-Lok tails (as would be installed by a touring company) and when budget permits the theatre can install a wall panel with Cam receptacles so there won't be a need to open the switch to tie in.
The electrician claims the wiring comes from a breaker, so the box need not be fused. He says, "they cannot be fused twice."
I quoted NEC 520.51:
IV. Portable Switchboards on Stage
520.51 Supply.
Portable switchboards shall be supplied only from power outlets of sufficient voltage and ampere rating. Such power outlets shall include only externally operable, enclosed fused switches or circuit breakers mounted on stage or at the permanent switchboard in locations readily accessible from the stage floor. Provisions for connection of an equipment grounding conductor shall be provided. For the purposes of conductor derating, the requirements of 520.27(B) shall apply.
I think the underlined areas in the code quoted above make it clear but I want to get my argument organized. So I'm wondering what the compelling reasons are to fuse the box--of course it seems safer--but what are the specific issues that can be addressed in this conversation?
Many thanks to the group.
In our example, there is a 100A 3-phase (4 wire + ground) feed to the stage, which is directly wired from a 100A 3-pole breaker in a separate panel. That panel is in another room.
The box they have installed (which I am questioning) is a simple safety switch with no internal fusing. For budgetary reasons, the client needed to go this route instead of installing a pre-manufactured theatrical company switch, which would of course have its own breakers. The switch is located onstage where it would only be operable by qualified personnel. It is likely that the first uses of this power source will use temporary Cam-Lok tails (as would be installed by a touring company) and when budget permits the theatre can install a wall panel with Cam receptacles so there won't be a need to open the switch to tie in.
The electrician claims the wiring comes from a breaker, so the box need not be fused. He says, "they cannot be fused twice."
I quoted NEC 520.51:
IV. Portable Switchboards on Stage
520.51 Supply.
Portable switchboards shall be supplied only from power outlets of sufficient voltage and ampere rating. Such power outlets shall include only externally operable, enclosed fused switches or circuit breakers mounted on stage or at the permanent switchboard in locations readily accessible from the stage floor. Provisions for connection of an equipment grounding conductor shall be provided. For the purposes of conductor derating, the requirements of 520.27(B) shall apply.
I think the underlined areas in the code quoted above make it clear but I want to get my argument organized. So I'm wondering what the compelling reasons are to fuse the box--of course it seems safer--but what are the specific issues that can be addressed in this conversation?
Many thanks to the group.