Surge breaker located in a separate structure

[mark32]

Hey guys,

A friend had a detached garage remodeled into a nicely finished hangout area for himself, complete with a split a/c system. Towards the end of the summer, the a/c compressor went bad, at least according to his a/c guy (Initially he thought a circuit board had went bad) He replaced the condensing unit and told my friend he should get some form of surge protection for it to hopefully avoid this issue again. Because the panel is flush mounted, I installed a surge breaker. This breaker only has a neutral lead coming off of it, and as the instructions say, just terminate it to the neutral bar. On the way home, it dawned on me that perhaps I should have landed that lead on the ground bar because, at least, there are two ground rods directly outside this structure. The feeder coming from the house (Four conductors) has an estimated length of 80'. So, should I leave this neutral lead connected to an 80' neutral conductor, or would it be better for the sake of his equipment (At the detached structure) that I terminate it to the GEC/ground rods via the panel's ground bar ?

 

[Little Bill]

Hey guys,

A friend had a detached garage remodeled into a nicely finished hangout area for himself, complete with a split a/c system. Towards the end of the summer, the a/c compressor went bad, at least according to his a/c guy (Initially he thought a circuit board had went bad) He replaced the condensing unit and told my friend he should get some form of surge protection for it to hopefully avoid this issue again. Because the panel is flush mounted, I installed a surge breaker. This breaker only has a neutral lead coming off of it, and as the instructions say, just terminate it to the neutral bar. On the way home, it dawned on me that perhaps I should have landed that lead on the ground bar because, at least, there are two ground rods directly outside this structure. The feeder coming from the house (Four conductors) has an estimated length of 80'. So, should I leave this neutral lead connected to an 80' neutral conductor, or would it be better for the sake of his equipment (At the detached structure) that I terminate it to the GEC/ground rods via the panel's ground bar ?

Just curious, what is the brand of the surge breaker?

 

[MasonF]

If the instructions said land it to the neutral then 110.3(B) would require you to follow those instructions. That would be the code requirement. As far as the effectiveness im sure someone else can add more but i assume the company designed it specifically to work off the grounded conductor if the directions said so and it should have an earth reference through the mbj at the house.

 

[wwhitney]

. . . it should have an earth reference through the mbj at the house.

The concern, of course, is that for the case of an elevated local earth reference (nearby lightning strike, say), the circuit path would be along the feeder grounded conductor, through the house MBJ, back along the feeder EGC, to the local GES. A longer, higher impedance path than just directly to the local GES.

Are there panel surge protectors available that are designed to be installed L-G, N-G, L-G, rather L-N, L-N? At a service panel, it makes little (no?) difference because of the MBJ, but at a remote structure as in the OP, it could.

Cheers, Wayne

 

[jim dungar]

Very basic: That plug on style surge device operates when there is an excessive voltage difference between the grounded conductor and the Line conductors. The grounding conductor is not part of the scheme so N-G protection is not offered.

Most non-plug on style devices offer N-G protection so they come with 4 wires.

I would leave the plug on device in place and add an inexpensive 4W hard wired device at the A/C.

 

[petersonra]

Hey guys,

A friend had a detached garage remodeled into a nicely finished hangout area for himself, complete with a split a/c system. Towards the end of the summer, the a/c compressor went bad, at least according to his a/c guy (Initially he thought a circuit board had went bad) He replaced the condensing unit and told my friend he should get some form of surge protection for it to hopefully avoid this issue again. Because the panel is flush mounted, I installed a surge breaker. This breaker only has a neutral lead coming off of it, and as the instructions say, just terminate it to the neutral bar. On the way home, it dawned on me that perhaps I should have landed that lead on the ground bar because, at least, there are two ground rods directly outside this structure. The feeder coming from the house (Four conductors) has an estimated length of 80'. So, should I leave this neutral lead connected to an 80' neutral conductor, or would it be better for the sake of his equipment (At the detached structure) that I terminate it to the GEC/ground rods via the panel's ground bar ?

What good would wiring it to the ground bar do? The GEC and GES does not really do much for you as far as surges go.

 

[mark32]

Thanks for the replies!

Little Bill, this is a Sq D QO panel.

As masonf and wwhitney have alluded to, the length of the neutral conductor is at the center of my concern. Concern because, whenever you read about these "Whole home" hardwired surge protectors, it's very obvious the leads from the protector should be as short as possible when being terminated within the panel, it's like each inch matters. I think it's implied/assumed that this device is going to installed in a main panel, which is not the case here.

Thank you Bill for the explanation, however, I'm still unsure how well this surge protector will perform when it needs to. As a side note, I just ran into a fellow electrician and I told him about this install. Turns out he just installed surge protectors right at the disconnect for his own a/c's. "How'd ya do that?" I quizzed. I was unaware, but on the market is a surge protector that comes in an fs box, and you can wire it into the circuit at the disconnect. Whether that would serve me better here is in the air; regardless, that would be for the next time I'm asked to protect an a/c, maybe

 

[mark32]

And thank you Petersonra. I have limited knowledge/experience with surge protectors. But in years past, it was my understanding that the job of a surge protector is to divert a surge into the ground. At the main panel everything is bonded together, so my thinking is that a surge can be routed to the water pipe and ground rod(s). I know they also absorb some (Or most?) of the surge, and in turn destroying itself.

 

[jim dungar]

And thank you Petersonra. I have limited knowledge/experience with surge protectors. But in years past, it was my understanding that the job of a surge protector is to divert a surge into the ground. At the main panel everything is bonded together, so my thinking is that a surge can be routed to the water pipe and ground rod(s). I know they also absorb some (Or most?) of the surge, and in turn destroying itself.

They do not divert a surge into the ground unless they have a large voltage to ground.

Surge protectors usually work by creating a short circuit across the conductive path effectively forcing the voltage to zero. Your plug on 3wire device "prevents" excessive voltage from developing between the line and neutral protecting the 120V loads, like your A/C circuit board. You would typically not experience elevated neutral to ground voltages unless the lightning strike was imposed after the neutral to ground bond at your service panel, which is definitely possible although it is not probable.

 

[gar]

221004-2045 EDT

You need to understand how a device works that you apply in some fashion.

The usual transient limiters with which you work are probably a non-linear resistive element that can be approximately described as two circuits back-to-back in parallel with one being of reverse polarity to the other. The net result is a two terminal device. One half of this parallel combination is a series circuit that can be approximated as a battery in series with a diode, and a series resistor.

The battery is the threshold voltage of the limiter defining where it starts to conduct, the resistor is the incremental resistance after conduction starts, and the diode limits current to one direction.

The battery voltage is a fixed value based on initial design, the incremental resistance is a function of the physical size, and is inversely proportional to physical size.

One could design a device that would work like an SCR. Here impedance is very high until triggered. When triggered the impedance goes very low, and voltage drop across the conducting SCR goes to a couple of volts.

MOV transient limiters will have a large voltage rise after their threshold is reached if there is no external current limiting impedance. So it is wise to have an MOV close to the load being protected to take advantage of the source impedance coming to the load. It is also wise to have voltage limiting earlier in the circuit, for example at the main panel, for external transient pulses.

Various limiters are needed between different wire pairs to limit the most damaging sources.

.

 

[mark32]

Thank you Jim and Gar!

It's funny that even after being in the trade for almost 30 years, doing residential, commercial, and industrial, I've rarely used surge protectors. The only time I recall installing them was when I worked at an airport (MCO) and we put them on the high mast poles scattered about the property (Lots of lightning strikes there!) And Gar, I haven't spent much time on the forum in a few years, so busy with other things, but I poke my head in from time to time. At one point I searched for a couple of favorite members, and unless I am mistaken, it appeared you had been inactive as well.