Relays to shed branch circuits

[iwire]

If the NEC doesn't require it, then the NEC is lacking, in my opinion.

Why? Because "off" should mean off.

So put in a proposal to ask for the change, the NEC does not change on it's own.

To the NEC off means off if it says 'off', as a disconnecting means does.

On the other hand controllers are not the same as disconnecting means and people working on electrical systems should be qualified to do so. Part of that training means understanding that unless you check .... nothing is off.

 

[iwire]

Why would you trust a relay/contactor as your disconnecting means? I sure wouldn't. Thing could close at any time. I prefer the single pole. It encourages use of the required disconnect.

Mark

+1 for commonsense.

 

[busman]

+1 for commonsense.

I might have to print and frame that.

Thanks Bob.

 

[tallgirl]

My problem is sheding loads off of my 200 amp service when having parties. Would like to shed water heater first, then hot tub followed by select select central airs. Likely far more money than practical. Situation is I have tripped the 200 main breaker and even melted triplex drop in two. Been converting what we can to propane. Goul would be to back loads off enough to stay under about 160 amps. Proplem is only for 6 hours each week when we need plenty of AC to cool about 100 people and about 3600 feet of rooms. Items such as range or cooktop is not in the picture as they are off.

If you have a current threshold on one circuit (including a feeder to a subpanel or a main panel) that you'd like to be used as a trigger for other circuits to be dropped, I can provide that.

The base cost starts around $500 for the embedded box that does the monitoring and sends the control signals and another $150 to $200 for each monitored circuit and another $150 to $200 for each controlled circuit. In your case, for probably obvious reason, the circuit to be monitored, and the circuit to be controlled, aren't the same circuit. The software is also able to turn off a circuit "softly" so that the current through the circuit must be below a minimum value before the contactor is opened. These prices are in the worst-case range -- the more you buy, the cheaper everything gets.

My vendor is =supposed= to have UL listing on the 20A AC contactors I spec, but if not, I support relay drivers that can be used to control listed contactors up to whatever capacity you can imagine.

 

[tallgirl]

Did some simple load shedding with my first plc project. We had way more HP than service.

If you loved that project, you'll LOVE working with solar. I have clients who try to run swamp coolers AND well pumps AND a house full of appliances on one 29A 120V inverter.

 

[Jim W in Tampa]

If you have a current threshold on one circuit (including a feeder to a subpanel or a main panel) that you'd like to be used as a trigger for other circuits to be dropped, I can provide that.

The base cost starts around $500 for the embedded box that does the monitoring and sends the control signals and another $150 to $200 for each monitored circuit and another $150 to $200 for each controlled circuit. In your case, for probably obvious reason, the circuit to be monitored, and the circuit to be controlled, aren't the same circuit. The software is also able to turn off a circuit "softly" so that the current through the circuit must be below a minimum value before the contactor is opened. These prices are in the worst-case range -- the more you buy, the cheaper everything gets.

My vendor is =supposed= to have UL listing on the 20A AC contactors I spec, but if not, I support relay drivers that can be used to control listed contactors up to whatever capacity you can imagine.

Thanks, I sorta figured it would be costly. Cheaper for us to either upgrade service to 320/400 or get water heater and hot tub onto propane. Have balanced out our loads better and not had problems in several months. Would assume the system uses a CT to triger the load. Will see how this summer goes before spending that much. Maybe POCO believe me if i melt another triplex. Does little good to have 200 amp service with wires rated for 160 amps.

 

[mrickey]

Does little good to have 200 amp service with wires rated for 160 amps.

QFT. When I upgraded my service this spring from 100A to 200A, POCO just reconnected the old #2 triplex to my new 4/0 AL SE Cable. Just doesnt seem like it should be allowed.

 

[LarryFine]

QFT. When I upgraded my service this spring from 100A to 200A, POCO just reconnected the old #2 triplex to my new 4/0 AL SE Cable. Just doesnt seem like it should be allowed.

That's what load calcs and Load Letters* are for.

*As our POCO calls them.

 

[SAC]

Regardless of NEC you'd probably be better off disconnecting both of the ungrounded conductors. This way you won't need to worry about different installs for 240v/120v appliances vs. purely 240v appliances (esp. since it isn't always obvious). Sometimes the multi-voltage appliances behave unpredictably when only one leg is lost.