[warrenhthelines-co-nz]

Hi. We purchase our DDOs with a drop down earthing connector attached outside the MAD. Elsewise on legacy DDOs where there are bare jumpers we will earth on the jumpers.

The airgap <300 mm is no issue as long as no action (eg earth clamps) need to enter that zone.

[Lance Brown]

Good afternoon Warren

Thank you for your response.

[Bill Doig]

We fit new EDO’s with earthing spigots so they’re below the stated distance. We don’t allow snap on earths to be used in these situations as when pushing the clamp off, there’s a risk of contacting the live side of the EDO

[Lance Brown]

Good afternoon Bill

Thank you for your response

[Stephen Small]

We are the same as WEL (Bill’s answer).

Note that there have been two previous EEA SSPG determinations on MAD distances for DO fuses, I don’t know if they are still searchable using the publications tab?

Stephen.

[Lance Brown]

Thank you, Stephen, I will search for it.

[Graeme Johnson]

Bang on there Mr Small, great memory.

This is the intepretation given back in 2002, still stands today. I also have a video of applicaiton of earthing that i made a few years ago that I’ll post up as link here.

Interpretation on Rule 703 and Minimum Approach Distances

Background

An interpretation was requested on the Minimum Approach Distance (MAD) requirements of SR-EI rule 703.

The specific issue involves working on the de-energised contact of a DDO when the line termination is energised. In this circumstance the de-energised contact is only 270mm from the energised contact, whereas rule 703 requires a MAD (for 11kV) of 300mm.

Interpretation

MAD’s as prescribed in rule 703 are minimum distances within which an employee must not encroach. The rule applies to any part of the body of the person, and to anything which is in contact with the person, other than a live work tool rated for the voltage. (Note that a temporary earth is not a live work tool).

The distances are established by taking into account the following;

· The behaviour of electrical power systems under steady state and transient conditions

· Determining the distances in air necessary to avoid electrical flashover under these conditions

· Providing additional allowance for inadvertent movement of the person and/or the electrical equipment

For 11kV the distance requirements for electrical considerations only are up to 66mm. The balance of the MAD is provided for inadvertent movement.

It should be noted that the standard Australian requirements for 11kV are for a MAD of 700mm for all persons. (They require a minimum distance for inadvertent movement of 600mm in all circumstances). This distance can be reduced under very controlled conditions, provided the person is ‘authorised’, ie competent.

DDO’s

The Safety Strategy & Policy Group has recently considered the MAD as applied to DDO’s as a result of an issue brought to its attention which involves the application and/or removal of temporary earths to lugs fitted to DDO’s. Such application or removal of the earth requires encroachment within the MAD. The SS&P Group confirmed during its considerations that the MAD’s provided in rule 703 are the minimum to be applied.

This matter is dealt with in the June issue of the Safety Rules Newsletter.

Conductors Connected to DDO’s

The MAD applies only to the distance of the employee (and any tool held) from the nearest live conductor, or live part. Work on a conductor which has a termination within the MAD is safe provided the break between the live and de-energised conductors meets the minimum distance for electrical flashover purposes, and the conductor being worked on is isolated and earthed.

Interpretation issued by EEA Safety Strategy & Policy Group

17^th July 2002

[james prime]

Hi Lance

We had this problem a number of years ago on what we term “22kv Bullhorn Carriers” with the first solution being to temp install hangers made from bent earthing rod and then hang the earth underneath but as this in not a clamped connection it is not suitable to carry any fault current. Now we use “Cut Out Earth Clamps” from Transnet installed with a shotgun or insulated stick. Further moving the earths away from the top live side and creating a clamped connection.

https://www.transnet.co.nz/Cutout-Earth-Clamp

Before this guys were hanging the earths directly on the lower carrier hanging point encroaching on the minimum gap to the top live side and also bending the lower hanger of the carrier.

I hope this relates to the question asked.

Cheers

• This reply was modified 1 week, 1 day ago by  james prime.

transnet.co.nz

Cutout Earth Clamp

DescriptionDesigned to attach to the bottom contact of an EDO and allow Temporary Earths to be safely applied when the EDO isn't fitted with an Earth Spigot.Earthing attachment is easily applied with a Shot Gun Stick.Fits both existing and new … Continue reading

Transnet-Cutout-Clamp.png 155 KB Image File - Click to view

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[Lance Brown]

Good morning James

Thank you for your response.

[Graeme Johnson]

Link to video = https://youtu.be/PcLPPL67MoA

[Lance Brown]

Good morning Graeme

Thank you for your response. The video is helpful and describes the scenario clearly, this will definitely aid in our team discussions.

Thank you again