Semi-Enclosed Rewirable Fuses

There is a lot of misperception in the industry as to whether the old ceramic fuses are still legal to remain in your switchboard.

The below article references clauses within Australian Standard AS/NZS 3000:2018 that guides all electrical work across Australia. Some minor variations occur in different states and territories, and this would need to be clarified within each state.

This document clarifies some of that misperception and provides guidance on repairs, additions and alterations to your electrical circuits, however it is written from the perspective of rules within NSW.

Semi-Enclosed Rewirable Fuses

What are the rules regarding semi-enclosed rewirable fuses in old homes?

You have asked me to do some work on your electrical system, perhaps add a power point, or light fitting, but your switchboard has old ceramic fuses as circuit protective devices.

What are the rules?

  • Can I add something to that circuit?
  • Must I replace the fuse?
  • Must I replace the switchboard?

The Australian Standards AS/NZS 3000:2018 is being referenced for these responses.

I’ll first start at Section 2 of the rule book.
This relates to: General arrangement, Control and protection.

The first clauses are very clear:

2.4.3 Types of devices
* Semi-enclosed rewirable fuses shall not be used
 2.5.2 Devices for protection against both overload and short-circuit Currents
* Semi-enclosed rewirable fuses shall not be used.

When making an alteration or addition to a circuit in a switchboard, where a semi-enclosed rewirable fuse is used, this must be replaced.

Ok, so that seems pretty clear. The old ceramic rewirable fuses can’t be used.

But… perhaps not.

Under the notes section it states:

2.5.2 Devices for protection against both overload and short-circuit Currents
NOTES:
3) Circuit-breakers that meet the requirements for the type of protection required and replace a fuse-carrier by insertion in a fuse base are acceptable. However, because of interchangeability with semi-enclosed rewirable fuse-carriers, such circuit-breakers should be rated at not more than 80% of the current-carrying capacity of the protected conductor.

If I make an addition to your home, I cannot reuse the rewirable fuse – this is clear. I can however remove the rewirable fuse and insert a plug in circuit breaker, but I may have to downgrade your circuit protection rating (change a 20A fuse to a 16A circuit breaker for instance); this could cause tripping due to overload.

This will depend on the rating of your conductor (cable), not the rating of your existing fuse – this is sometimes misunderstood by electricians.

It is definitely NOT an ideal outcome, and I would not recommend using plug in circuit breakers. This is because they can be mixed up by homeowners with an incorrect size being inserted. This can cause melting cables and fires (which is why rewirable fuses are now banned). However, it is the difference between $100 or more (add an extra $200 or so if there is asbestos present). Compare that to around $20 for a plug in circuit breaker.

If we are unsure of the cable ratings of the old imperial cables, we can check Appendix I, which provides guidance on current ratings of old cables. We can then match a circuit breaker to the installation style indicated in the table provided.

What about repairs?

  1. Your power point (light fitting, oven, etc.) blows up and you need a replacement. Do I still need to replace the rewirable fuse with a circuit breaker?

No – see below

  1. Your rewirable fuse base burns and your electrician has a spare. Can he/she replace the base?

Yes, but this is a bit more complicated.

If an electrician has a recovered fuse and fuse base (saved from a previous job) he can fit a replacement of the same type.

However, fuse bases are no longer available for purchase, in which case if one is not available a new circuit breaker or RCBO must be installed. An RCBO (Residual current Circuit Breaker with Overload protection) is an individual safety switch that also contains overload protection.

However…

A circuit breaker (CB) can only be installed where an RCD (Residual Current Device – safety switch) is present. While it would take another two pages of references to show rules, repairs must be like for like. Installing a CB would be considered an alteration, and therefore an RCD or an RCBO must be fitted (only if an RCD is not current present on that circuit).

RCBOs are preferred over RCDs due to a reduced likelihood of nuisance tripping, and greater reliability long term.

So, let’s confirm this by looking at Section 1 of the rule book:

1.4.8 Alteration A modification to part(s) of an electrical installation.
NOTE:
Repairs are not alterations. A repair is defined in Clause 1.4.101.

The note above is very important. It states that Repairs are NOT alterations. Alterations are considered to be the same as new work (Additions).

This means that the rules noted in section 2 and appendix I noted above are not relevant, unless there is a concurrent alteration/addition.

1.9.3.2 Repairs
Repairs to existing electrical installations or parts there of may be effected using methods, fixtures and fittings that were acceptable when that part of the electrical installation was originally installed or with methods….

So, I can repair your electrical system with equipment (if available) that is equivalent to that which is currently installed, providing that it was compliant when first installed and still available (whether salvaged or purchased).

I hope that this clarifies our legal requirements regarding alterations, additions where rewirable fuses are present.

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