Installing Major Tech MTD8 Timer Switch: Wires etc

Good day.

Quick question…

I’m in the process of self installing a MTD8. It’s meant for my geyser. 3kW Geyser sits on a 15A breaker. The cable feeding it from the DB is this white thing, looks like what people call Surfix (two cores with an earth running down between them all ensconced in said white sleeve). This cable is longer than it needs to be as geyser was moved.

So…Can I just trim off the ends and use them in my DB wiring of MTD8 to circuit breaker and MTD8 to Neutral buss-bar?

This makes sense to me but I don’t want to be a lunatic, not here at least.

Random question:
If my cable feeding the geyser is about 8m too long looping around would this effect efficiency significantly?


It’s common practice, for sparkies, to take a piece of twin-and-earth (that’s what it sounds like), strip off the outer sheath, and use the red and black wiring for other purposes.

If I understand you correctly, you have a piece of twin-and-earth, I assume of the correct thickness, running into your DB, and you want to know if you can use an off-cut from this to get the wiring you need to wire up the timer switch, which I presume is also going to be installed in the same DB.

It should be fine to do this, but I would strip off the outer part and use the individual conductors for the wiring from the breaker and neutral bar to the timer switch. I would not use unmodified twin and earth from the breaker/neutral bar to the timer switch.

Yes, it will affect it. No, it will not affect it significantly. Leave the extra length, it bothers nobody and you never know when you need it.

Hey Plonkster

Yes, that is what I meant…that whole paragraph. And the next paragraph was what I intended.


Can I suggest that you rather install this system: Geyserwise TSE Geyser Controller | Parow | Gumtree South Africa
This will do the job a whole lot better and all for such a reasonable price :money_mouth_face:
Those small timers can’t handle the current of geyser elements over time…

What will happen?

So anyway. I’ve done it without frying myself. That’s good news.

Something did happen though…

I had dropped the circuit breaker of my geyser to climb into the attic and fiddle with some wires (previous individual had made a real rat’s nest of splicing lengths together). There’s a 30A switch up there, looks like a fat light switch. I had not dropped the Earth Leakage nor Mains switch though. While I was busy rewiring this 30A switch the Earth Leakage on the DB tripped…Why is that?

That 30A switch is called an Isolator switch. It is used by the plumber to isolate the geyser when he needs to do work.

Geyser must have a double pole switch at the geyser so that whoever works on the geyser, can switch it off at the geyser. Also to protect the person working there, in case someone switches the main breaker back on at the DB.

Right, sorry…my question was unclear:

Seeing as I had dropped the circuit breaker at the DB how come when I was fiddling with this Isolator Switch, which is downstream from the DB, did the Earth Leakage trip?

Does this make sense?

You probably touched the neutral wire to earth while working on things. It is that simple.

Longer explanation. When you turn off the breaker, it only isolates the live. Neutral is still connected to the supply. Neutral is at the same potential as ground, so generally not considered to be dangerous, but it is a current carrying conductor that is still connected to the supply, and it is capable of conducting a small amount of current. When you touch it to ground, eg when pulling it out of the hole in a metal box/fitting, a couple of milliamps decides to take a shortcut through this new temporary TN bond you created, thereby bypassing the RCD and causing an imbalance, which trips it.

Doesn’t matter if this is at the end of a long cable and it really isn’t a “shortcut”, a few stupid electrons will take that path.

In other words, no need to worry. This is perfectly normal. It proves your RCD still works.

That clears it up…I did notice this happened when the wires were all up and in the air and i was moving stuff around


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Hence the double pole 30a switch at the geyser, to stop nuisance tripping on the main DB.

They can’t handle the current (even though the specs indicate they can)
Open it up to see the size of relay they use…

Yeah, but he was working on that very switch itself… :slight_smile:

Missed that. Sparkie and plumber, when they work on that switch, they always switch off the main DB … and keep it off till they personally come and switch the main DB back on. Luckily the geysers are not on Critical Loads.

After my last bout of shocking myself, complacency breeds contempt comes to mind, I’m so gatvol with myself now that I refuse to work on anything AC anymore.

When I replaced the MP, it did not count, after the main DB was off I contemplated on how to switch off the house in the street box, then to find the transformer in the suburb and switch that off … then speak to Eskom to help a bud out.

Cause between having had Covid and shocking myself properly two days in a row, I wondered it all somehow related to me “having to go for a quick spin in intensive care”.

I’m leaning the other way these days. The last time I replaced a socket in this house, I actually did it live. I would of course not do that if any wires have to be pulled through holes, but sometimes the whole “getting permission” thing takes too long. Takes longer than just getting the job done.

Now that I know that an RCD trips if neutral touches earth, I will also simply tape off the neutral while working on it, rather than switch off the entire house… and then having to reset all the clocks, etc etc.

Of course this is firmly in that “do as I say, not as I do” category. I’ve watched enough sparkies do these very same things :slight_smile:

Yeah … that’s what I did … just a quick thing man … you’ve got this … don’t touch that red wire, the DB won’t trip.

I hate it when my arm starts tingling with 220v AC. HATE it!
The fright is the worst.

Geez, the 2nd time it happened, the next day, I was at the gate working on a light there. The sparkies arrived that instant asking what all the swearing was about. Told them, you are 2 days late, the earth leakage does not work … there, you #($*% finish this … I’m done!

They hosed themselves … :rofl: