Why Does Neutral & Ground Short Together in AC Circuits?

[monus76]

hi there
need help

i just need to know why ground and neutral ( A.C CIRCUITS) short together on the body of machine chassis or panels.i found this in one oil heating unit ,with high wattage of heating element.

who ever can reply ,highly appreciated

with thanks

 

[Averagesupernova]

It depends on when the installation was done. New installations should never have the neutral and ground hooked together except in the main service entrance. Any subpanel, disconnect for a furnace, air conditioner, etc. must keep the neutral and ground seperated. In the past, the neutral and ground were allowed to be shared or connected in subpanels. Search physics forums for this sort of thing. It's been discussed before.

 

[m.s.j]

In low voltage systems, the three main grounding system are used as defined in IEC 60364:

- Exposed-conductive parts connected to neutral -TN-
- Earthed neutral -TT-
- Unearthed (or impedance-earthed) neutral -IT-

The purpose of these three systems is identical as regards protection of persons and property mastery of insulation fault effects. For choosing the best grounding system, it is important to know our requirements and resources.

For more information you can refer to Grounding riddle No.21 in http://electrical-riddles.com