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Posted By Topic: Should I be providing overload protection

Oct 27 2019 20:00

I was trying to work out whether I needed to provide overload protection at the main switchboard for mains so I contacted the local supply company

I am in Christchurch and the supply company is Orion

They responded to my email saying they provide short circuit protection and that they provide "HRC 63amp short circuit"

I don't know a lot about HRC fuse types but can anyone advise me on if I should be providing overload protection at the switchboard? I mean they certainly made it feel like they only provide short circuit protection but the 63a part threw me off


Oct 27 2019 23:03

63a HRC fuse will provide both overcurrent and short circuit protection for the mains.

Oct 28 2019 00:21

The 63A supply fuses are generally accepted as providing overload protection.

You could use a 63A MCB as a main switch if you wanted to, but it probably won't provide any discrimination with the 63A fuse. But if the installation ever got into an overload situation, would it really matter?

Oct 28 2019 07:10

Thank you, I wasn't sure if this one was a bit of a silly question but was aware there was different types of fuses and just the way they worded things made me doubt it a bit

Oct 29 2019 17:43

It's not a silly question. It's one of the quirks Orion have on there network. They'll want a 60 amp MCB prior to the meter. You'll need to provide your own 'overload' protection. If your doing some sort of changes to the mains, or if it's a new connection and it's on Orions network, they'll want you to fit an MCB or HRC fuse prior to the meter.

They say their service fuse is only suitable for short circuit protection and you need to sort overload protection yourself. Even though as mentioned, their 63 amp fuse, will serve as both overload and short circuit protection.

My guess as to why they do this has something to do with liability. If something goes wrong due to overload current then it's not their responsibility. Guess it also means they don't have to be so critical about the size of their fuse, as long as it's rated for short circuit.

Read ESR 32. It more or less says a person supply a line function (Orion in your case) to a customer, only has to provide short circuit protection (not overload).

Oct 29 2019 18:27

Nickg. Can't seem to find those details in here?

Oct 29 2019 18:40

Yeah, I've noticed it's not mentioned in there, I don't know why. It's mentioned in another one of their documents 'network connection guidelines'. Don't know if that's public information or not though. It's definitely a requirement though, most guys that are regularly working on Orions network are pretty familiar with it now.

Oct 29 2019 21:38

Yeah it's a real odd one, I thought maybe it was a type of HRC that only does short circuit? As I've heard they exist but like I've said never really dealt with HRCs much

I've tried to get some more information out of them so shall see how we go

They certainly made it confusing

Oct 30 2019 09:01

i suspect it's simply that this linesco is putting ypu on notice that overload protection is your responsibility. Most sparkies appear to be unaware, and just rely on the network to protect their mains. And mostly it works, because most networks use s/c & fault protection by HRC fuse sized to limit the load to no more than the contract supply capacity.

If the fuse is rated 63 A, that's its rated CCC and it will provide overload protection for any mains with CCC 63A or more.
By asking you to install another fitting, they leave themselves the future option of changing the fuse to an isolation link, and providing s/c & fault protection by some other means.

In Oz, some networks provide s/c protection on upstream (HV)side of the tx; and they don't always provide fault protection. Which is why several clauses in "3000" refer to "unprotected consumer mains"

Oct 30 2019 12:25

Got some confirmation, they use a 63A HRC fuse type gG

Technically they said this does provide both overload and short circuit protection but they only say they provide short circuit because they require the overload protection to be placed in the installation

That's all I needed to know, I'm happy to provide it, I just wanted to know the basis behind it and got confused when they started saying '63A HRC' but also saying 'short circuit protection only'

Oct 30 2019 14:40

Did they explain to you how to achieve discrimination?

Oct 30 2019 15:17

No they didn't, I enquired about it but they said something about they couldn't provide a current time curve for some reason, didn't really make sense

Oct 31 2019 09:35

In practice at this level it won't be an issue.
Speaking from an embarrassing experience years ago, where I drilled through a beam into a final subcircuit, tripping the 63A C-curve mcb but not blowing the 63A Gg supply fuse.

But the info on both fuses and mcbs is available on interweb for anyone who wants to do the exercise


Nov 04 2019 15:32

NickG do you know where to find the other document you mentioned? "network connection guidelines"

Might send them an email and see if I can get my hands on it

Nov 08 2019 08:04

Sorry, late reply. Yes contact someone from Orion. See if they can supply you with a copy of their ‘connection and livening guide for LV installations’ the details are in there.

You’re probably best to contact one of the inspection companies that work as agents to them, they’ll be able to help you.

Have a look in a meter box next time you’re in one of the newer developments about town. You’ll see what I mean. Standard single phase 60 amp supply, will most likely have a 60 amp MCB installed in the box prior to the meter.