The TMB
plug is the same as a standard pin
plug in all respects except for a larger cable entry hole.
Here's an important
point: many safe things we do in the
theatre are different from "normal" electrical practice. The
NEC helps us with this. Chapters 1 through 4 of the Code are general requirements for all installations. Chapters 5 through 8 modify or extend those requirements for special occupancies or applications. A
theatre is a special occupancy covered by Article 520.
Here's a
clear example of how Art. 520 can change a "standard" requirement:
Here are a few sections from Chapter 4 relating to connectors:
400.10 Pull at Joints and Terminals.
Flexible cords and cables shall be connected to devices and to fittings so that tension is not transmitted to joints or terminals.
Exception: Listed
portable single-pole devices that are intended to accommodate such tension at their terminals shall be permitted to be used with single-conductor flexible cable.
FPN: Some methods of preventing pull on a
cord from being transmitted to joints or terminals are knotting the
cord, winding with tape, and fittings designed for the purpose.
406.6 Attachment Plugs, Cord Connectors, and Flanged Surface Devices.
All attachment plugs,
cord connectors, and flanged surface devices (inlets and outlets) shall be listed and marked with the manufacturer’s name or identification and
voltage and
ampere ratings.
(A) Construction of Attachment Plugs and
Cord Connectors. Attachment plugs and
cord connectors shall be constructed so that there are no exposed current-carrying parts except the prongs, blades, or pins. The
cover for
wire terminations shall be a part that is essential for the operation of an attachment
plug or
connector (
dead-front construction).
(B) Connection of Attachment Plugs. Attachment plugs shall be installed so that their prongs, blades, or pins are not energized unless inserted into an energized
receptacle or
cord connectors. No
receptacle shall be installed so as to require the insertion of an energized attachment
plug as its source of supply.
(C) Attachment
Plug Ejector Mechanisms. Attachment
plug ejector mechanisms shall not adversely affect engagement of the blades of the attachment
plug with the contacts of the
receptacle.
(D) Flanged Surface
Inlet. A flanged surface
inlet shall be installed such that the prongs, blades, or pins are not energized unless an energized
cord connector is inserted into it.
406.7 Noninterchangeability.
Receptacles,
cord connectors, and attachment plugs shall be constructed such that
receptacle or
cord connectors do not accept an attachment
plug with a different
voltage or
current rating from that for which the device is intended. However, a 20-ampere T-slot
receptacle or
cord connector shall be permitted to accept a 15-ampere attachment
plug of the same
voltage rating. Non–grounding-type receptacles and connectors shall not accept grounding-type attachment plugs.
These sound pretty sensible, right? Different
ampacity plugs cannot be interchanged, strain must be kept off
connector termination points. All good?
Sure, but what about a single-pole
Cam-lok connector that has no separate
strain relief, and allows ampacities of 100 to 400 amps to interchange?
Here's how Article 520 deals with it:
K) Single-Pole Separable Connectors. Where single-pole
portable cable connectors are used, they shall be listed and of the locking type.
Sections 400.10, 406.6, and 406.7 shall not apply to listed single-pole separable connectors and single-conductor cable assemblies utilizing listed single-pole separable connectors. Where paralleled sets of current-carrying, single-pole separable connectors are provided as input devices, they shall be prominently labeled with a warning indicating the presence of internal parallel connections. The use of single-pole separable connectors shall comply with at least one of the following conditions:
(1) Connection and disconnection of connectors are possible only where the supply connectors are interlocked to the source and it is not possible to connect or
disconnect connectors when the supply is energized.
(2)
Line connectors are of the listed sequential-interlocking type so that load connectors shall be connected in the following sequence:
a. Equipment
grounding conductor connection
b. Grounded
circuit conductor connection, if provided
c.
Ungrounded conductor connection, and that disconnection shall be in the reverse order
(3) A caution notice shall be provided adjacent to the
line connectors indicating that
plug connection shall be in the following order:
a. Equipment
grounding conductor connectors
b. Grounded
circuit conductor connectors, if provided
c.
Ungrounded conductor connectors, and that disconnection shall be in the reverse order
So, it's important to be careful about invoking "standard" electrical code requirements without knowing if they have been modified by the special occupancy articles, as in the above example.
ST