DIN-Rail mounted 230VAC LED indicators are quite useful to show that mains power is connected to a sub-DB or an inverter output is active.

My question is - does one need to install a fuse or circuit-breaker in series with this type of LED indicator? An electrician pointed me to Chapter 7.4.6.7 in SANS 10142-1 - which suggests that this is needed. My interpretation of this requirement is that it only applies to temporary DBs at construction sites.

I can understand that a fuse/breaker may have been important when using old incandescent bulbs, but these LED indicators should be internally current-limited and inherently safe. They typically just have a Cap and Resistor in series with a back-to-back LED/Diode. The X-Class Cap will only pass a limited current even when directly across mains. The series resistor will instantly fuse if the cap is somehow short circuited. Unfortunately I cannot find any such current-limit/fusible specification on any of these LED indicators (Hager, Schneider, ABB, Siemens etc.).

Also, I was hoping to use thinner wire (e.g. 1.5mm^2) to connect the LED indicator to the incoming mains supply (10mm^2).  My reasoning, which may well be incorrect, is that one does not need to protect this thinner wire against a high-current short-circuit condition since the Indicator LED effectively includes a fusible element or has a limited fault current.

Any thoughts?

 

1 hour ago, NigelL said:

Any thoughts?

My thoughts are that as long as the wires going to it re thick enough to carry the current required to trip the upstream breaker, you're done. But I am not an electrician.

I was also hoping to avoid that 🤔. I guess I will have to do it, but it just seems a rather inelegant solution given that the LED Indicator is a device with an inherently low-value fusible current. But still better than having to install an additional circuit breaker just for the LED Indicator!

I noticed that in some official wiring diagram somewhere for the Carlo Gavazzi ET112 meter, it also shows a fuse in the neutral wire. This is a pretty similar situation: All the real power flows through the thick red wires, the black wire is there only to supply the meter itself with power, and it needs milliamps at most. I'm just not sure what the best way is to do it... if you have DB space you could fit a single din-mount fuse of course.

16 minutes ago, plonkster said:

.. if you have DB space you could fit a single din-mount fuse of course.

I guess that I have just re-discovered one of the immutable laws of the universe, that applies to many different fields.

Actual_DB_Space_Required = Planned_DB_Space + n (where n >= 1). 😃  

23 minutes ago, NigelL said:

Actual_DB_Space_Required = Planned_DB_Space + n (where n >= 1).

I ran into that problem recently, and the cost to rewire to make more space was silly.

In the end I got a surface mounted DB, for the dedicated circuits I want powered on batteries.

Also learnt that if you get a DB that has plugs in it, the costs drop more, because what you plug into those 3 point plugs, is none of the electricians business.

That was useful to my particular needs, saved a bit on that, as I had separate circuits already in place to the points I want stuff powered.

Similar to this, I just have 3 plugs in the DB: