What kind of readings could you possible get between the phase conductors to ground if the main bonding jumper was left out. Lets say for example 120v/240v single phase system to a Modern residential home. Does the power company bond the neutal at the transformer on the pole? I would say yes, So my thoughts is that it would all depend on resistance of the ground to the pole. Can anyone help me understand this better? Thanks
Possible voltage readings if Main bonding jumper is left out.
- Thread starter JdoubleU
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
A lot depends on the install. The poco does ground their neutral and it is bonded in the meter can as well. If there is metal conduit between the meter and the panel then the panel is in fact bonded also. However if non metallic raceway or cable is used then the can is not bonded and theoretically there would be zero voltage to the can as it is isolated from the neutral.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It depends on the impedance of your measuring device.
If you are using a digital meter, it is extremely likely you will 'read a voltage'.
meternerd
Senior Member
- Location
- Athol, ID
- Occupation
- retired water & electric utility electrician, meter/relay tech
Our utility bonds the neutral to ground at the transformer. There is no ground wire run from the transformer to the service. The main bonding jumper installed at the service disconnect bonds the neutral, panel, ground rod and any metal conduit at the meter panel. If the MBJ is not installed, any voltage readings will depend on resistance from the panel abck to the pole ground. Could be anything depending on meter impedance, system load, etc.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is always possible to get some voltage reading, especialy with a digital meter, which is due 'coupling capacitance'.
In the simple case yes -- the secondary is isolated form the earth so the earth should not have any voltage reference to the transformer output. But there could be a capacitive coupling effect which shows up on a meter. But try to run something with "normal" impedance from a transformer wire and earth and that voltage will disappear to zero.
Also be careful with power company transformers. Many times, both the primary and secondary are bonded and grounded at the pole (so every pole with a transformer is part of the grounding system). The utility supply always has a voltage to earth whether you connect it to earth again at your distribution panel or not.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Resistance will not change the voltage unless there is current flowing. IOW if you have an open circuit you will not have any voltage drop and will read the full applied voltage.
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