multiple neutral-earth connection, so what?

crancreature

If my pure sine inverter has an internal neutral-earth bond, and my AC load center has a neutral earth bond as well, so what? They will be parked a foot away from each other, if the short green ground wire between them provides a parallel path, so be it, I'll label it "hot" or something so the next owner won't be too taken by surprise. In effect I will pretend the load center and the inverter are one single unit, and that short stretch of parallel path--one foot of green wire same size as the white--it will not affect anything out in the house, right? Codes are no concern in my case, only safety. I understand the multi-bond problem in general, but why the concern if the inverter and panel both have bonds? (Also, fully off-grid basic system, inverter designed to be hard-wired, I realize I may have some trouble with the outlets on the inverter but don't plan to use those.)

Another multiple bond assumption by me: my internally bonded Kohler electric plant generator will be located in separate building, the ONLY thing it will be connected to in the house in an Iota charger, it will not be connected to the inverter or the AC in the house anywhere. I don't have the Iota yet, but I assume it will use the generator's cable for it's earth, and its DC side is electrically isolated/different from AC side. (I will be bonding the DC to the earth rod at the batt negative.) There is no parallel path to be had (right?), my generator will be bonded AND my house load center will be bonded, but since they're separated by the charger and the batteries, they might as well be in different counties.

So, I think my system will have three different neutral-earth bonds, might even have four because I may add some separate circuits with another inverter (and a separate load center).

I'm not trying to make it hard or strange, I just don't want to go about opening cases and control boxes and unbonding everything, and I'm not actually sure my inverter is bonded inside (manual unclear, thus my insistence on also bonding inside the load center), but in all my reading on this site, I think I understand the principles about multiple bonding points and nothing I propose merits a red light.

Thanks for responding, this is my first post but have lurked for a long time on this site, the breadth of knowledge here is interesting and humbling to me.

vtmaps

Re: multiple neutral-earth connection, so what?

crancreature wrote: »

and I'm not actually sure my inverter is bonded inside (manual unclear, thus my insistence on also bonding inside the load center)

Welcome to the forum,
Turn off the inverter, disconnect the inverter from everything, use your ohmmeter to measure the resistance between neutral and ground. If it's zero, you're bonded.

crancreature wrote: »

Another multiple bond assumption by me: my internally bonded Kohler electric plant generator will be located in separate building, the ONLY thing it will be connected to in the house in an Iota charger, it will not be connected to the inverter or the AC in the house anywhere. I don't have the Iota yet, but I assume it will use the generator's cable for it's earth, and its DC side is electrically isolated/different from AC side. (I will be bonding the DC to the earth rod at the batt negative.) There is no parallel path to be had (right?), my generator will be bonded AND my house load center will be bonded, but since they're separated by the charger and the batteries, they might as well be in different counties.

You better check that assumption. Even if the Iota output is isolated, you are setting yourself up for lightning problems. When lightning strikes in the neighborhood, your multiple ground rods can be 1000's of volts apart. That means your Iota input and output will be 1000's of volts apart. Sparks will fly inside your Iota.

This same effect is what causes submersible well pumps to burn out... the pump casing is grounded to the well, but the wires inside the casing are grounded at the house. Sparks will fly between the internal wires and the casing.

--vtMaps

NorthGuy

Re: multiple neutral-earth connection, so what?

When you have two neutral to ground connections, both wires between these connections bewcome a common electrical path. When there's a common path between the grounding system and AC system, the signal from one may get injected into the other.

Say, you have a lightning which dissipates through a grounding system. It is a huge current, and even though the common path has very low resistance, this current will create a voltage potential accross the common path. This means that you will have a voltage spike in your AC system. May damage something.

Similarly, the signal from the AC system may be injected into a grounding system, which may affect TV reception or make your radio hum. It's probably not a big deal because everything is digital now.

crancreature

Re: multiple neutral-earth connection, so what?

Ohmeter reads no resistance between all leads (without power to it). I don't know if this is meaningful. Dimensions Sensata. The actual ground rod is a well casing, a single point, connected with star pattern type philosophy. So, bonding in multiple locations but grounding only going to earth in one, with the philosophy of eliminating voltage differences of lightening. Still, I'm mulling over what you both are saying about burning out the Iota with voltage differences in a lightning storm, the earth wire to ground rod would have to be insulated and heavy gauge and still might not work, so if I unbond the generator, then... anyway, glad I asked, but so far not seeing why the short distance between inverter and load center could be a problem, this may be OK?

NorthGuy

Re: multiple neutral-earth connection, so what?

crancreature wrote: »

... but so far not seeing why the short distance between inverter and load center could be a problem, this may be OK?

If lightning current is 10kA then a 10 mOhm (0.01 Ohm) resistance will produce 10000*0.01 = 100V voltage spike. What is 0.01 Ohm? It is, for example, 25 feet of $6 wire. But this is an oversimplification. Such high currents travel through the wires differently, so I don't know if Ohm's law applies here. These are just theories.

waynefromnscanada

Re: multiple neutral-earth connection, so what?

crancreature wrote: »

Ohmeter reads no resistance between all leads

Just to clarify any possible misunderstanding - - by "no resistance", do you mean less than one ohm resistance, or do you mean resistance so high the meter doesn't record it?

Thanks
Wayne

crancreature

Re: multiple neutral-earth connection, so what?

I think, to solve the lightening problem, the generator, if remains internally bonded, then all its earth wiring including the casing of the generator, need to remain separate from the actual earth (buried inside PVC) until it ties in at the point of the "star" of my grounding rod (well casing) where it then becomes grounded. This means in the event of nearby lightening, no voltage difference can be acquired, there is only one place where earthing is occuring--at the well casing. I hadn't planned on that (would have buried bare copper and perhaps left the genset directly on the pad).

There will be NO parallel path of shared neutral/ground on my generator system, the green wire to my Iota is in no way tied into the house system, it is separated from the house system by the batteries and the DC system, the only place neutral touches earth will be at the genset which will acquire its earth value from the well casing (not the surrounding nearby earth) I don't think it violates the principles of multiple points of bonding because it is separate from what is going on in the house.

I think my inverter WILL violate the principle of multiple points of bonding, but its only a foot away from the load center, what harm is there, I could build a casing to cover the inverter+load center and call them the same appliance--no one could criticize that, or is there some concern I haven't realized?

crancreature

Re: multiple neutral-earth connection, so what?

less than one ohm, needle leaps to 0 as though I touch both leads of the meter together.