Elevated electrcial fields

[bakmpn]

I am an electrical engineer working on a parking lot pole lighting design/installation whose poles are located about 90 feet horizontally away from the mid span of a horizontal arrangement of 230 KV 3 phase transmission lines. The poles are positioned outside of the easement for these HV lines. The HID flood lighting fixtures are specified to be mounted to bullhorn mounting brackets atop fiberglass poles 25 ft Above finished grade.

While trying to make the 208 volt single phase circuit splices in one lighting pole handhole the electrician was experiencing shocks. There were no circuit connections to the building power panelboard when he was experiencing the shocks. I am aware that there can be induced voltages in metal objects that are ungrounded in the vicinity of HV lines. Also I am aware that the electric fields can approach 2KV/m under the mid span of HV lines of the KV indicated above. High enough to illuminate a handheld 4 foot fluorescent tube.

Other than moving the poles further away from the lines, can placing the circuiting entirely in metal conduit (flexible) within the pole and(rigid metal) underground to the grade junction box as well as placing supplemental ground rods at the base of the poles to which the conduit and the equipment ground conductors are connected help attenuate the electric field on the circuiting? If the electric field can be shielded will the ballasts still function properly?

 

[ken987]

Re: Elevated electrcial fields

A company I'd worked for maintained the electrical systems at a local app complex
with 230KV lines running right through the middle of the complex, fiberglass poles were used on this installation for the street lighting.
Don't know if this helps you,that's what they had done.

 

[hurk27]

Re: Elevated electrcial fields

From the first post:
atop fiberglass poles 25 ft Above finished grade.

Someone didn't read the first post throughly.

But in installations like this it must be required that the circuit conductors be connected to a grounded source before doing the connections at the pole's, This will ensure that the EMF will be kept at a very minimum. A grounding conductor routed with the ungrounded conductors will cancel most EMF out as long as it is bonded first before the poles are connected,just keep in mind that even these connection's can have a voltage potential when these grounding bonds are made at the supply and should be treated as they are live HV and maybe a bonding jumper with clips be used to temporally bond each conductor before making final connection. Ground rod's will help but not as good as a bonded grounding conductor will. And metal conduit will help keep the voltage off the conductors but the conduit itself will become energized. Maybe bonding the grounding conductor before rolling out the feed to the poles would help.
I worked at a plant the had this same problem but with everything metal! Fencing, piping, rails, even isolated metal roofing. We just made it mandatory to bond any isolated metal to the service grounding and ground rods. We had jumper cable bonds laying out in the stock yards to keep the loose metal stock from being energized. Again there was transmission lines running right next to the plant and partially over the stock yard.

Does the state have any EMF pollution laws that would require the utility's that own these transmission lines to accept some of the responsibility of the extra cost they are causing?

 

[bakmpn]

Re: Elevated electrcial fields

Thanks Wayne A. for the response! For clarification when you say a grounding conductor I assume you mean an equipment ground conductor which is bonded to the neutral only at the service entrance. The HID ballasts operate from 208 volt single phase and no neutral is required to operate the ballast.

 

[hurk27]

Re: Elevated electrcial fields

Yes I did mean a EGC. I should of said that in my post but even though the fixtures operate from 208 a EGC still has to be ran with th ungrounded conductors to each pole and bonded to the fixture's grounding terminal. Just make sure it's connected at the building first.