? Risk Of Installing Electric Flow Through Water Heater

[mayview]

I have 2 Stiebel Eltron h/w shower heaters that I wish to substitute for older units.

The two independent power sources both have RCB switches in the line supply. Both units are earthedr back to the Supply unit and tested.

The two new h/w heaters have these safety devices incorporated.

Should I remove the standalone RCB switches from the lines? Is there any risk of having additional RCB's on the same line?

[BuckarooBanzai]

Having an additional high quality RCB switch in line with an appropriate leakage setting is a very good idea.

[lopburi3]

As said the second RCB will provide protection for any contact prior to the installed unit (the lines) as well as back-up for installed unit.

[mayview]

Having an additional high quality RCB switch in line with an appropriate leakage setting is a very good idea.

Thankyou. It stays!

The previous line RCB has a 15mA sensitivity I don't know the h/w heater spec for this.

Edited July 28, 2012 by mayview

[mayview]

As said the second RCB will provide protection for any contact prior to the installed unit (the lines) as well as back-up for installed unit.

Great to have a confirmation reply on this aspect. Grateful

[Crossy]

Yes, leave the existing RCD in place, it can do no harm and (as others have noted) protects you from shock from dodgy joins in the cable.

Do verify that your existing breaker and cable are man enough for your new heaters if they are are of higher power than the existing ones.

[mayview]

Yes, leave the existing RCD in place, it can do no harm and (as others have noted) protects you from shock from dodgy joins in the cable.

Do verify that your existing breaker and cable are man enough for your new heaters if they are are of higher power than the existing ones.

5 sq mm cable.

25 amp Type C CB's.

4.2 KW heaters.

Hoping this is OK?

[Crossy]

5mm² is an unusual size, are you sure that's what's installed? The common sizes are 1, 1.5, 2.5, 4, 6, 10, 16, 25, 35 mm²

A 4.2kW heater will pull around 20A so it would be OK (just) on 2.5mm² which is what's often installed.

[electau]

Install 6.0sqmm cable with a 25A or 32A RCBO for the final circuit. Earth the heaters using a minimum of 2.5sqmm green or green /yellow insulated conductor. The RCBO should have a sensitivity of 30mA.

You retain the existing RCD in the heater. This will only disconnect the heater in the event of an earth fault on the load side of this protective device.

2.5sqmm is permissable as it has a 25A rating under certain installation conditions.

[lopburi3]

Believe 2.5, as you say, in this case should be fine as run should be short and such heaters are normally only used a few minutes a day and seldom at full rated power.