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Posted By Topic: aerial clearances

Mar 31 2018 14:03

Hi customer has one insulator on point of entry about to fall off .
customer has had the line company remove the pole fuse removed and i have refixed the insulators into sound timber . on tensioning up the aerial connectors the max height i can get is 3.7 meters.They were lower than that to start with . Table 3.8 gives clearances of 3.0m for areas not used by vehicles . And 4.6 for areas used by vehicles. This aerial connection is for a barn in a rural address, it crosses a grazing paddock, so primarily not for vehicles .... but a tractor could quite conceiveably drive under.
OK or not ?

Mar 31 2018 14:18

The table in 3000 for aerial clearances assumes a public road in which the maximum height of any vehicle is 4.3 metres plus a margin to allow for wind or temperature sag.

In the farm area you are considering the maximum height that could in some circumstances e.g. a tractor with hay bale lifter could exceed 4.3 metres, hence the minimum aerial height becomes whatever the naximum height vehicle that could go under the line plus a margin to allow for wind or temperature sag.

Apr 02 2018 08:00

here there is often confussion with clearance of over head conductors. AS/NZS 3000 has its own clearance but ECP 34 also has listed clearances but quite different. The Regulations refer to the ECP 34 os clearances required. So would this not be the document used as the regs out weigh the standards

Apr 02 2018 09:50

Yes ESR 17 cites ECP 34 for maintaining safe distances from electric lines (also ESR 70 for inspecting HV). And yes ECP 34 includes minimum height of "service mains"; but that term is now out-of date, and important to realise that ESR 17 does NOT cite the ECP for mains of installations.

The situation here is clearly installation wiring, not lines; which are defined in the Act as being "works. Accordingly "3000" applies (via ESR 59), and ECP 34 does not. It's installation wiring because it is downstream of the point of supply; which will be either the pole fuse (if on-site) or the point where the mains cross the boundary.

Table 3.8 of "3000" does NOT "assume a public road"; in fact clause specifically excludes public roads. Which is entirely logical, because "3000" is about installation wiring - and while there can be installations on public roads they are very unlikely to have any overhead wiring that is part of the installation.

The term "areas used by vehicles" covers driveways etc, where vehicles are likely to be used. It doesn't necessarily apply just because a vehicle might possibly be used there. That becomes a judgement call based on the expectations at time of installation. The open front of a hay-barn would be expected to have vehicles; a closed wall of the same structure in the same paddock could well be considered unlikely to have vehicles. The rule is designed around normal vehicles, not fork-lifts and other vehicles that may have unusual height. Where such equipment is regularly used, obviously the minimum heights could be insufficient.

In addition, the clearances set by Table 3.8 are for new work; whereas these o/h conductors are existing, and presumably were originally installed long ago. Noting that if they were installed at a time when ECP 34 was the appropriate reference (between 1993 and 2010); as the "last span connected to any building" and "in places likely to be used by vehicles" the required height would have been 3.5 m, reducable to 2.7 m for non-vehicle and to 2.5 m if both conductors insulated. So they would have complied.

There is no requirement to raise the conductors. However if use of vehicles, especially tall vehicles, is likely on any regular basis; consideration should be given to either raising and/ or (probably better) re-locating to reduce the chances of contact. Use of a high-visibility warning system could also be considered


Apr 02 2018 17:25

thanks every one for your considerd detailed replies.
I've checked the height of the john deer tractors commonly used by farmers . 2.93 meters seem to be the height .So 3.7 M should be ok.