to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Special Installations
  --1. - Introduction --2. - Bath tubs and shower basins
  --3. - Swimming pools --4. - Sauna rooms
  --5. - Installations on construction sites --6. - Agricultural & horticultural
--7. - Restrictive conductive locations --8. - Earthing for function & protection
--9. - Caravan, motor homes, caravan parks 10. - Highway power & street furniture
11. - Heating appliances & installations 12. - Discharge lighting
13. - Underground & overhead wiring 14. - Outdoor installations & garden buildings
15. - Installations of machines & transformers 16. - Reduced voltage systems
17. - Marinas 18. - Medical locations
19. - Exhibitions, shows and stands


7.11.2 - Electrode boilers and water heaters

An electrode heater or boiler is a device which heats the water contained, or raises steam.

Two or three electrodes are immersed in the water and a single- or three-phase supply is connected to them. There is no element, the water being heated by the current which flows through it between the electrodes. Electrode heaters and boilers must be used on a.c. supplies only, or electrolysis will occur, breaking down the water into its components of hydrogen and oxygen. The different requirements for single-phase and three-phase boilers are shown below.

A - Three-phase heaters fed from a low voltage supply {Fig 7.13}

Fig 7.13 Three-phase electrode heater fed from a low voltage supply

The requirements are:

1. - a controlling circuit breaker which opens all three phase conductors and is provided with protective overloads in each line,

2. - the shell of the heater bonded to the sheath and/or armour of the supply cable with a conductor of cross-sectional area at least equal to that of each phase conductor,

3. - the shell of the heater bonded to the neutral by a conductor of cross-sectional area at least equal to that of each phase conductor.


B - Three phase electrode heaters fed from a supply exceeding low voltage {Fig 7.14}

Fig 7.14 - Three-phase electrode boiler fed from a supply exceeding low voltage

The requirements are:

1. - a controlling circuit breaker filled with residual current tripping, set to operate when the residual current is sustained arid exceeds 10% of the rated supply current. Sometimes this arrangement will result in frequent tripping of the circuit breaker, in which case the tripping current may be reset to 15% of the rated current arid/or a time delay device may be fitted to prevent tripping due to short duration transients. See {5.9} for more information concerning residual current devices,

2. - the shell of the heater must be bonded to the sheath or armour of the supply cable with a conductor of current rating at least equal to the RCD tripping current, but with a minimum cross-sectional area of 2.5 mm˛.


C - Single-phase electrode heaters {Fig 7.15}

Fig 7.15 - Single-phase electrode heater

The requirements for single-phase electrode heaters are:

1. - a double-pole linked circuit breaker with overload protection in each line,

2. - the shell of the heater bonded to the sheath and/or armour of the supply cable with a conductor of current-carrying capacity at least equal to that of each live conductor,

3. - the shell of the heater bonded to the neutral,

4. - the supply must be one which has an earthed neutral.


D - Insulated single-phase electrode heater, not permanently piped to water supply

Fig 7.16 Insulated single-phase electrode heater, not piped in to a water supply

This small heater is usually fixed in position, but is filled by using a flexible hose or a water container.

The requirements are:

1. - there must be no contact with earthed metal,

2. - the heater must be insulated and shielded to prevent the electrodes from being touched,

3. - control must be by means of a single-pole fuse or by a circuit breaker and a
----- double pole switch,

4. - the shell of the heater must be bonded to the cable sheath.

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations