non continuous loads on a branch circuit

[petersonra]

Thank you all for being so generous with your expertise. The existing system is in fact wired with all 6 devices (dock locks) on a single 20amp breaker, and has been since installed in 1996. No one ever recalls a breaker trip. However, I am at this time upgrading these lock controllers, which causes me to review the install to ensure it's code compliant. It seems that, although incredibly unlikely, technically to comply with code, I can't put more than two devices per breaker. I understand sometimes what's practical, and what's legal don't always align. Is there any provision in the code that allows for a deviation based on local engineer review? Seems like I remember seeing something like this before.

You have a choice between code compliance and non-compliance.

I ran into a similar thing once. Had some MV CB's that had motorized operators. The motor only runs for a few seconds at a time, but all five operators were supposed to trip simultaneously under a few cases. Each motor was like 20 Amps at 120 VDC. Five motors = 100 Amps at 120 VDC needed. And only used a few seconds at a time a few times a month.

 

[jap]

Thank you all for being so generous with your expertise. The existing system is in fact wired with all 6 devices (dock locks) on a single 20amp breaker, and has been since installed in 1996. No one ever recalls a breaker trip. However, I am at this time upgrading these lock controllers, which causes me to review the install to ensure it's code compliant. It seems that, although incredibly unlikely, technically to comply with code, I can't put more than two devices per breaker. I understand sometimes what's practical, and what's legal don't always align. Is there any provision in the code that allows for a deviation based on local engineer review? Seems like I remember seeing something like this before.

Since the locks are now getting a 2nd look after all these years, In addition to practical or legal I would consider if it is actually a good design to have all the locks on 1 circuit.

Much like LED lighting.

Yes you can load up and put a ton of lighting on 1 circuit, but, If that circuit does happen to trip for some reason, do you actually want that much area to go dark?

Maybe, maybe not.

JAP>

 

[winnie]

I think that jap has a good point. If the circuit does fail than perhaps it is better to have only half of the docks out of service rather than all of them.

On the other side of the coin, it would probably be pretty simple to interlock the loads so that they can't run at the same time.

Yet another option is to have lock controllers with some amount of energy storage, so that they don't have such high peak current. (Eg. keep a battery charged to actually run the dock lock motor, and only load the circuit with the battery charger input.)

-Jon