Sorry if this has been covered before - couldn't find anything at a quick glance.
If using passively safe poles on an ELV installation do you still use the break away plugs and if so what is the justification. There is no real need for electrical isolation anymore so is it better to allow the pole to break free than to keep it tethered by the cable?
my understanding is that the even though the guidance states you don't have to electrically isolate the pole you should still consider it - worst case scenario syndrome. As long as you cover yourself with the relevant RRRAP and supporting documentation you should be ok.
In terms of the breakaway plugs, my belief is that it's better to allow the pole to break free than to have it tethered by the cables. The guidance is pretty vague on this and 'helpfully' it leaves most of the decision making down to the design engineer!
If you speak to the HA, they don't (or certainly didn't) regard the risk of secondary accidents to be high enough to argue against the use of passive poles and pole breakaway units.
The view is that the potential risk to the driver of the vehicle coming into contact with a non-moving pole with 50kilos of signal heads etc attached to it is much greater than the potential risk of the pole causing a secondary accident by breaking away into oncoming traffic.
Don't shoot the messenger - this is just what I have been told when in conversations with various HA representatives.
The method of electrical isolation you need for a passively safe pole should be governed by your choice of pole, due to the different ways these are designed to operate in the event of a vehicle strike. For poles which are designed to shear or breakaway on impact, then the use of the pull-out plug will achieve electrical isolation and give the additional benefit of not tethering the pole in the event of a vehicle strike. For poles which are designed to yield on impact, but not breakaway, it may be found that an alternative solution provides a more appropriate method, such as an inertia sensor (as used in vehicles to actuate fuel cut-offs) mounted within each pole to activate a circuit breaker mounted in the controller or MEC to isolate the pole. Consult the pole manufacturers to find out which method of isolation they’ve used in order to pass the crash tests for product approval.
Breakaway poles.
You'll find that in most situations where passive poles do break on impact, it is due to vehicle speeds being reasonably high, the poles tend to break at ground level, the vehicle passes under the (now) airborne pole and signal head (or sign etc), then falls to the ground behind the vehicle approximately where it was installed. The whole idea is that the transfer of energy from the errant vehicle to the pole assembly is kept to a minimum. Also not all passively safe poles are designed to break on impact.
Please find the article I wrote for the engineers handbook regarding these issues attached.