replacing old fuses

[pedro the swift]

A question to any household sparkies out there. I am considering updgrading my switchboards which has old porcelain fuses. I want to install combo RCDs and MCBs.
Just not sure what to replace the existing power and light fuses with in regard to current rating.
The old power fuses are rated at 16amp and lights at 8amp. I can get 16 amp MCBs and 10 amp MCbs for the lights. I thought it would be possible to replace the 16 amp fuses with 20 amp MCBs since they operate faster.
Question: what is the suggested replacement rating for these items?

By the way , I am a licensed electrician. Just havent been involved in domestic work for many years.
Thanks in advance for your replies.

[floobyduster]

I'm not up with the specs, but what is the current rating of the house wiring? It's not just a matter of the speed of the MCBs.

[b1ueshift]

I don't think that's correct because MCB's work on thermal trip similar to a fuse. I know they trip lightning fast when you get earth leakage, but the overcurrent protection seems to be a slow thermal trip - which is all you need because cables can tolerate overcurrent for a short time without overheating.

I think it's standard practice to use 16amp MCB's for power point circuits and 10amp for lights.

[Pulse]

Pedro, AS3000 has a table of conductor size and allowable circuit breakers for different installation conditions, as long as you stick to that it chould be OK.

Cheers
Pulse

[pedro the swift]

Hmmm, thanks for the replies. I am pretty sure the wiring for power is 2.5msq so 16amp will be the go. But I will check again.
Blueshift, yes MCbs do work on thermal but nearly all of then also have a magnetic trip for instant break on short circuit condiditons. The idea being you can get a slow increase in load up to the thermal rating without causing a magnetic trip. Gives protection for a majority of conditions. Earth leakage is a different system again. Works by measuring the difference in current flow in the active and neutral of the protected circuit. Any differnce over the limit and off it goes( we hope).
rgds

[Markw]

The old rules used to say that if replaicng with a breaker, it was allowable to go from 10 to 16A?? on lighting circuit and 16 to 20A on power circuit.

But this was the AS 3000 rules for a few years back. Recent changes I believe refer to wire sizes in sq mm as the method of calculation.

Nothing is ever easy as it used to be.

Then again if you need to ask this question you shouldn't be doing the work. You can change the ceramic fuse to a push in HPM breaker without changing the holder but to change to K rail box with miniture breakers is best left to the qualified.

[pedro the swift]

Markw, thanks for the words of wisdom. Thats how I remember it also.
I dont really want to go for the mcb inserts in the old fuses holders as I feel its not a step forward.
I asked the question for a reponse from some sparkies who do this sort of work on a daily basis.
I have held electrical licenses in three states for many years but havent been crawling under houses or in roofs doing house wiring for a long time. I work in a different electrical field but still use my license for that.
Since there seems to be no clear cut answer I will do the research and come to my conclusions as to whats required.
Thanks

[titand]

Hi Pedro,

I'm sure that with your qualifications you can safely do the job but I'd be interested to know what legal qualifications you need in Queensland?

Can anyone confirm that in Victoria, the Nanny State, even a fully qualified Electrician needs to have either an Owner-Occupiers license or be working under a Registered Electrical Contractors (REC) license, either their own or their employers, to do work at home because he or she has to submit a Certificate of Electrical Safety and I think only a REC can do that?

I'm sure its all for the best...

[b1ueshift]

I think the answer to your question is yes - in practice you would need to be an REC.

The electrical safety act in Victoria has some extreme wording.

The electrical worker needs to issue a certificate to Energy Safe Victoria every time they do any installation, maintenance or repairs to fixed electrical equipment or face a $1000 fine.

[journeyman Mick]

My next door neighbour is a safety inspector for Ergon energy (our local supplier), he's a qualified, but not licensed electrician and he operates under his employer's license. When he built his house, he was allowed to do the work himself. Apparently in Qld qualified but unlicensed electricians are allowed to work on their own houses and those of their immediate family.

Mick