HW cylinder: am I about to be blown up?

[Mr Fizzion]

Some vodka bottles appear to be made of steel or aluminium. I wonder if you could make a steam "bottle rocket"? :-)

Mr F.

[Ed Sirett]

By the book, only qualified people should work on these units. However informed diy is better than leaving the an unqualified 'buffoon'.

Does this unit have an external (probably blue) pressure vessel? If not it is probably the sort that has an internal air pocket (Mega Flow and Telford & Elson are at least three makes like this.)

If it is an air pocket type then the air pocket will need to be renewed from time to time. There shold be instructions on the cylinder and probably in the installation book on this. Essentially turn the water off, allow water out and air in.

If you are not happy to work on it yourself then find someone who is qualified.

[Ed Sirett]

The explosion hazard whilst it is real present is not perhaps the greatest threat. The really large risk is that should the over pressure device fail then the next line of safety is the over-temperature device. The installation _must_ be capable of dumping the bulk of it contents of near BOILING water at full mains flow - Safely.

[Ian Stirling]

Though rarely at the same time.

[Matt]

Why oh why oh why, did they put it in a hole in the ground. Much more fun and more representative to have the blast above ground level.

Disgusted of Tunbridge Wells

[Mr Fizzion]

Not as fearless as you or I are they? :-)

Interesting that water heaters like that take 40 amps (in america)...seriously thick wire!

Mr F.

[John Rumm]

IIRC there was a pretty scary story in the book "Why buildings fall down" about how one took out a complete appartment block in the US.

[John Rumm]

You mean like 6mm^2? Bit like a low end electric shower then ;-)

[Christian McArdle]

Now that would be spectacular! It would have to be a great shot from a coastal property...

Christian.

[Christian McArdle]

Why 40A, it was only 4.5kW, which is about 20A. High current appliances are usually wired up at 240V in the US.

Christian.

[Jim Michaels]

Incorrect.

In America (well the US and Canada anyway) the standard electric water heater is 4500W ( 18.75amps at 240Volts). This requires a 25amp circuit due to a rule that requires continuous use devices to be run on circuits de-rated to 80%.

Higher performance units are 5500W (22.916 amps at 240Volts) requiring a 30amp circuit .

I think the sizes are historical from when the US/Canada nominal voltage was 230V (around WWII)

4500W 230V * 1.25 = 24.456amps 5500W 230V * 1.25 = 29.891amps

Both of these are normally wired with 10gauge wire (5.26mm2)

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