Electrical Ground Question

[BillyP]

I have poultry houses with some pretty expensive electronic equipment. It's not uncommon for electrical shorts to occur from time to time. The neutral and ground bars are bonded together inside the breaker box (3 wire system). Would it be better to separate the neutral and ground bars and run the ground bar directly to a ground rod?

 

[BB_TX]

The company I work for supplies control systems for power plants. They typically have two grounds. One is the standard green wire safety ground that eventually connects to neutral. The other is an "instrument ground" that is an isolated dedicated ground for protection of sensitive instruments. Yours may or may not have a connection point for such a separate ground.
Do you have surge protection on the power source for that equipment?

 

[techman]

To have a remote panel (seems like a subpanel), code (NEC) actually does not allow the neutral and common to be bonded in that panel. The reason is quite simple, neutral currents will start to flow through the ground line (since it is effectively paralleled with the ground line). This can cause the ground at the subpanel to have a potential above "real" ground (pipes, earth, concrete, etc). This means that you could feel some voltage between a socket wall plate and the kitchen sink.

There are some who think that grounding the subpanel to a local ground rod is a better way. If this is done and the two grounds are interconnected, additional ground circulating currents can occur, leading to more risk.

For safety and code the bonding should not be done in the subpanel, and only at the main service panel. If you are really worried about ground related surge issues (due to lightning, etc), the proper way is to feed the subpanel from a 1:1 isolation transformer. The sub can than be grounded locally and bonded. Best solution but can be quite expensive.

paul

 

[BillyP]

Yes, Bill, I do have inline surge suppressors just for the controllers. Thanks

 

[midlf]

If the panels are in separate structures the panel is treated by code as a service entrance and the neutral and ground need to be bonded together. My experience with problems in this area is the required grounding electrode, (the ground rod(s)) are not adequate. Also there may be too much of a potential difference between the panel and remote grounded metal. Separating the neutral and ground in the box may make your problem worse. The separate electronic neutral mentioned is to have a clean ground connection going from the equipment to the ground bar with nothing else connected to it to inject interference.

First step for me would be to install more ground rods. Depending on your soil and moisture conditions you may need quite a few to get the ground resistance down to a low level. The code specified 1 ohm is NOT adequate if you are having problems. I would also surround the building with a ground conductor and do what it takes to tie it into the concrete reinforcing or mesh if that is present.

 

[BillyP]

OK Paul, here's the deal. I have a 200 amp main (located under the electric meter) that supplies 2 poultry houses. Inside the control room is a breaker box where everything is wired to. (this is the one I'm talking about).

You say the neutral and ground shouldn't be bonded in this panel? If so, then wouldn't it have to be grounded by way of a ground rod?

I'm just trying to figure out which way would be best to protect my controllers.

 

[heehaw]

i will "assume" your electric meter/200 amp main, is not "on" either of the chicken houses: and you have 3 wires that run from that box to the breaker boxes at each house??? am i any where close to what you have??
heehaw

 

[BillyP]

I have 2 sets of 3 wires running from the 200 amp main, to 2 different panels

 

[SPIKER]

the 200 amp panel/disconnect under the meter is a considered the service disconnect for most of these types of instelations. the panel inside the chickencoups is then the primary panel for that building and each building by code requires to be grounded per NEC and the N and G bars to be bonded together in the panelboards. if you are having ground problems on specific items then you need to make sure the equipent with problems is first off have proper groudning to the equipment and as well any outside locations have to have GFIC installed. there are certain farm instances that DO involve aminal barns which I'm not up on and have changed this year (NEC2005 actually) bonding the concrete rebar/mess is good and will help isolate any floating grounds too. make sure all the connections are good as well. if ALUM wire was used make sure no corrosion exists and an anti0oxident was sued on the wire end connections..


anyhow I think I read you already have surge suppressors on there? if so make sure none of those are causeing problems as in burnt out or fused or open partly. using isolation transformers is EXPENSIVE but will solve problems but are generally only used in high buck places such as docoffice/hospitals.


anyhow hope this helps.

makrm

 

[heehaw]

what spiker said is correct, to expand on it a little, everything metal should be tied to the ground: i maintained a lot of electronic phone systems and communications radios on mtn tops for almost 30 years: and the main thing that seemed to make a real difference, was the addition of more gnd rods, and tying everything metal i could find, to the gnd: in one office, i even drilled a hole in the floor, directly under the phone system and drove a gnd rod: that system was still in and working when i retired last year, and had never been damaged by lightning: after 15+ years.
heehaw