House + Shop Ground Loop Avoidance

[kwschumm]

Please forgive me if this has been covered before, I didn't have much success searching.

We are building a new house and shop that are about 60 feet apart.

The 320A Electrical service will have one meter for both buildings, main service in house and subpanel in shop. Both buildings will share security, PLC lighting, network and a few surveillance cams connected to a single DVR.

Lightning will be an occasional issue so whole house surge suppressors will be installed in both buildings which will require short and solid grounds. Security system panels in both buildings require dedicated ground connections.

I'd like to have the electrical system installed so there are no ground loops between house and shop. What should I ask of the electrical contractors in order to have a grounding system that meets our needs?

Thanks in advance for all the shared expertise!

 

[wyliesdiesels]

This topic of ground loops has been covered before but it is a pharse.

Have you poured the slabs yet?

If not, will the concrete be in direct contact with the earth?

If so, make sure to do UFER electrodes.

You will need a 4-wire feed between buildings.

If lightning is an issue, i recommend utilizing fiber to tie the communication between the buildings together.

If fiber is not an option, utilize ethernet and other types of surge suppressors on any and all cables between buildings.

 

[kwschumm]

Designs are done, slabs can't be poured until spring due to the amount of dirt that needs to be moved (county regs). Garage and shop will be slabs but house will be a crawl space, with rebar footings of course. With two separate slabs I'd think maybe tying them together to one ground rod might be a good idea. No idea what NEC says about this.

The requirements of panel surge suppressors and security panels to have separate grounds is confusing:

2. GROUND THE CONTROLLER "EARTH GND" TERMINAL TO A COLD WATER PIPE OR TO A 4-FOOT GROUND ROD TO PRESERVE ITS BUILT-IN TRANSIENT PROTECTION. USE 14 GAUGE WIRE. TRANSIENT PROTECTION WILL NOT WORK IF THE CONTROLLER IS NOT PROPERLY GROUNDED.

Seems using a dedicated rod would be a source for ground loops, and water pipe will be Wirsbo.

There will be a separate low voltage conduit with various surge gadgets and opto-isolator repeaters on both ends.

 

[wyliesdiesels]

BOTH buildings are required to have electrodes.

You cant have just use one on the house for the shop especially with lightning.

You want the shortest path to earth for lightning.

Any additional rods you use for peripherials needs to be bonded to the GES for the electrical system so everything is at the same potential.

Where are you getting this idea of ground loops?

 

[kwschumm]

BOTH buildings are required to have electrodes.

You cant have just use one on the house for the shop especially with lightning.

You want the shortest path to earth for lightning.

Any additional rods you use for peripherials needs to be bonded to the GES for the electrical system so everything is at the same potential.

Where are you getting this idea of ground loops?

So you're saying that even though the two buildings have their own electrodes they will be at the same ground potential because of the ground cable connecting them?

After googling grounding I encountered two different stories, one said that the only electrode should be at the house panel and the shop was bonded to that, and the other was that each should have their own. To me it seemed that a single shared electrode would eliminate the possibility of ground loops.

To answer your question, I'm an embedded software guy (not an EE) and I've had some experience with connected control system hardware in separate buildings, and even separate floors of the same building, frying due to different ground potentials. We fixed with opto-isolators but I considered it a grounding problem.

 

[DC73]

. . . I've had some experience with connected control system hardware in separate buildings, and even separate floors of the same building, frying due to different ground potentials. We fixed with opto-isolators but I considered it a grounding problem.

You are correct in your thinking. The short answer is that the grounds for the two buildings should be connected together to avoid ground loops. Opto-isolators or fiber optic cables are another option.

When lightning strikes nearby, and there are two separate buildings with separate grounding points, the lighting strike creates a potential difference between the two grounding points. That potential difference causes electricity to flow through the ground between the two grounding points. However, if the two buildings also contain sensitive electronic equipment that are connected together with coax, CAT6, telephone cable, etc, those wires become the path of least resistance and frequently the resulting current is strong enough to fry the sensitive electronic equipment. Power companies are well aware of ground loops and the resulting damage caused by lightning strikes.

DC

 

[wyliesdiesels]

So you're saying that even though the two buildings have their own electrodes they will be at the same ground potential because of the ground cable connecting them?

yes and you want them at the same potential otherwise lightning can wreck even more havoc.

Also, code requires electrodes at all buildings for this reason.

After googling grounding I encountered two different stories, one said that the only electrode should be at the house panel and the shop was bonded to that, and the other was that each should have their own. To me it seemed that a single shared electrode would eliminate the possibility of ground loops.

To answer your question, I'm an embedded software guy (not an EE) and I've had some experience with connected control system hardware in separate buildings, and even separate floors of the same building, frying due to different ground potentials. We fixed with opto-isolators but I considered it a grounding problem.

yes Different ground potentials is caused by poor bonding. Im guessing there was poor bonding in that location...

Having a 4-wire feeder with electrodes on both ends will ensure equal potential.

And trust me, you want electrodes on both sides.

Think of it this way. Would you want lightning travelling all the way to the house from the garage if thats the only place you have electrodes?

Now dont get me wrong, lightning could still do that but the goal is to reduce the potential.

You also mitigate it with point of use surge suppressors and lightning arrestors...

 

[kwschumm]

Thank you gentlemen, this information is most helpful. I really appreciate it!

 

[sberry]

If both service come from the meter base how would be use 4 wire? 4 is normally used when adding a service from an existing service, is he simply going to add a 4th between panels?

 

[wyliesdiesels]

If both service come from the meter base how would be use 4 wire? 4 is normally used when adding a service from an existing service, is he simply going to add a 4th between panels?

Huh?

He didnt say anything like that.

Just said there will be one meter, MAIN SERVICE in house, subpanel in shop.

Nothing about 2 services off one meter base.

Main service and subpanel are the key words.

Go back and reread the OP.

 

[Stuff]

Tube amplifiers would use the neutral for ground (2 prong cord) which caused ground loops. Audiophiles have been blaming electricians for their problems ever since.

 

[matt_i]

If you are worried about lightning strikes I would definitely use the UFER ground. It has much more surface area than the rod(s) and thus a lower overall resistance, despite it being a seemingly non-conductive material like concrete. As I recall the initial research and resulting design was triggered to prevent munitions stockpiles from self immolating if lightning struck the area (especially in arid conditions). The lightning strike itself is unavoidable but having a low-resistance path to ground is best-case otherwise the massive flow of energy starts "looking" for additional pathways and that's where the damage starts....