Whole house surge protector. Can it be on a subpanel?

[lgmagone]

Last year, I hired a contractor to install an air conditioning system in our house. The electrician didn't want to put the 30a / 240v system on a subpanel because he thought it might overload the subpanel. The main circuit breaker panel is full. I suggested that he move the whole house surge to the subpanel, but he didn't think that would work either. Eventually, I suggested he disconnect the electrical connection for the dryer outlet (our house has an option for both gas and/or electric. We are using gas instead of electric).

My question is, if a future owner wants to use electric, would the whole house surge protector still provide whole house protection if located on a subpanel? I have done some Googling but haven't found a good answer. This would be good to know in case a future owner wanted to switch to electric dryer in the future.

NOTE: I'm a Professional Engineer, not a licensed electrician. I am not asking "how to" on this post. Rather, I'm asking, "is it appropriate to hire an electrician to do this task for me". The last licensed electrician didn't know, and I would like to know for sure for future reference.

 

[Mouser]

Connecting the SP in a downstream panel will not protect circuits upstream.

 

[petersonra]

Last year, I hired a contractor to install an air conditioning system in our house. The electrician didn't want to put the 30a / 240v system on a subpanel because he thought it might overload the subpanel. The main circuit breaker panel is full. I suggested that he move the whole house surge to the subpanel, but he didn't think that would work either. Eventually, I suggested he disconnect the electrical connection for the dryer outlet (our house has an option for both gas and/or electric. We are using gas instead of electric).

My question is, if a future owner wants to use electric, would the whole house surge protector still provide whole house protection if located on a subpanel? I have done some Googling but haven't found a good answer. This would be good to know in case a future owner wanted to switch to electric dryer in the future.

NOTE: I'm a Professional Engineer, not a licensed electrician. I am not asking "how to" on this post. Rather, I'm asking, "is it appropriate to hire an electrician to do this task for me". The last licensed electrician didn't know, and I would like to know for sure for future reference.

The SPD will give you some protection no matter where it is located. It works best when at the service panel. How much protection you lose by putting in another panel is not something I can quantify.

I am surprised the electrician did not just replace a couple of the breakers in the main panel with double breakers and use the space created to run a circuit to the AC unit.

 

[blkmagik21]

Those whole house surge protectors are supposed to even be placed on the bus bar closest to the breaker feeding the power.


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[lgmagone]

The SPD will give you some protection no matter where it is located. It works best when at the service panel. How much protection you lose by putting in another panel is not something I can quantify.

I am surprised the electrician did not just replace a couple of the breakers in the main panel with double breakers and use the space created to run a circuit to the AC unit.

The guy that did the quote for the job quoted it assuming that a couple breakers would be replaced with double breakers.

Then the electrician came out to do the job, popped a couple breakers out and decided they couldn't be replaced. I didn't follow the problem exactly, but I am thinking that part of the circuit breaker panel didn't have the right mounting hardware for double breakers. Or maybe it required a brand of double breakers that the electrician didn't have in his truck. I'm not exactly sure which.


It also baffles me why, when the house was being built, the electricians didn't put more circuit breakers in the subpanel, so there would be some empty slots in both the main panel and subpanel. The two are located right next to each other and there is plenty of room in the subpanel that they could have moved a few over.

No big deal though.

 

[kwired]

Is it a "plug on" protector (mounts in place of a breaker) or a "wired in" protector? Wired protectors often just get connected to same breaker as another circuit - electric water heater circuit is pretty common.

Have had a few cases with VFD well pump controllers where the well guy supplies one and requires it to be connected to same breaker as the well circuit. Kind of naturally becomes somewhat of a whole house protector in those cases, as that is the type of protector he is supplying. Just the other day had a HVAC guy hand me such a protector and wanted it on the circuit for his mini-split he was installing. Again somewhat becomes a whole house protector just because it is in there.

 

[Baeljb]

Distance

Distance

It is 100% dependent on the wiring distance between the main and sub panel. If adjacent to the main, no problem. If more than 20 wiring feet, then it will still work but protection will be compromised. The surge protectors work on being the point of lowest resistance/impedance on the electrical distribution. It has to overcome the resistance/impedance of the conductors between the main and the sub.

 

[gar]

180727-2011 EDT

To answer the question you need to understand what a whole house protector is, how it works, and what do you want to protect from.

These devices are at least a non-linear resistance relative to applied voltage. Relatively little current flows until some threshold is reached. The threshold has to be somewhat above nominal peak line voltage. For a nominal 120 supply you might want to pick 140*1.414 or higher for this threshold.

Once the threshold is reached the current for a given voltage rises rapidly as voltage increases. Find the i-v curve for a specific device to see how it is characterized. You may expect the protector to go a 100 or more volts above a 200 V threshold before voltage is clamped. How far in overvoltage the circuit goes is a function of the series limiting impedance, and available source energy.

If the source of transient energy is external to the main panel, then the limiter needs to be connected on the output of the main breaker. That is if the goal is whole house protection. It would be very useful if series inductance could be added before the main breaker.

You want the protector as close as possible to what is to be protected, and as much impedance as possible between the source of transient energy and the protector.

.

 

[junkhound]

Pretty much as mouser said.

'Some' protection downstream is very little, close to none.

Rise time of lightning is usually 6 microseconds with a typical current level of 20kA (some as high as a few mega amps, get hit with one of those and everything is literally blown away, arrestors and all)

Remember V=L* di/dt. di/dt = 20E3/5e-6 = 20E9, 20 billion amps per second.

Say subpanel is only 1 meter away, one rule of thumb is 1 uH per meter, so 1E-6*20E9 = 20 kV inductive drop : not much protection even if you have a 'perfect' arrestor.

Now put the arrestor just under half inch from main bus. Inductive drop is now reduced to about 200 volts vs. 20 kV. Obvious which is more effective.

 

[romex jockey]

methinks it somewhat an nfpa 780 Q, not something garden variety sparks are normally trained to

~RJ~

 

[goldstar]

Those whole house surge protectors are supposed to even be placed on the bus bar closest to the breaker feeding the power.


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If you're implying that the wires should be landed on the lugs ahead of the main breaker I don't thin it's a Code compliant installation. Most manufacturers state in their instructions that the device should be connected to a 2-pole breaker. If the device's wires are landed onto the main lugs ahead of the main breaker, while you may get the max protection out of the device, the lugs aren't rated for the additional wire. In addition, most manufacturers will state that the wires from the protective device should be landed on a breaker as close as possible to the main breaker.

If I interpreted your statement incorrectly I apologize.

 

[Adamjamma]

The way I read both of your statements is basically, use the upper left or right position for a two pole device. The opposite space would be reserved for a generator back feed if you were using an interlock system.
Unless your service breaker is at the bottom of the panel, which means use one of the bottom slots. In either case, it is a priority slot rather than put anywhere. If USA panels are still labeled the same after 20 years away, on a 24 box with main breaker above, we are talking slot 1 or 2.
The use of the double slot is so it covers both phases.
unless I misunderstand the technology.
I am simply a student again.