Voltage between neutral and ground 3

[edison123]

My friend is installing an elevator in his home. According to the company's commissioning engineer, the voltage between the neutral and ground should be less than 2 V but my friend's installation gives 3 to 3.5 V.

Is the eleveator engineer right in insisting on less than 2 V ? Is there any standard for power supply to elevators ?

* I would go green if only I were not yellow *

 

[ESOXmaniac]

Hi- You are faced with one of either two problems or issues. Neutral to ground voltage has traditionally been used as a figure of merit to judge available power quality. This has largely been promoted promoted by those who make isolation transformers/power quality equipment. However, the reality of what the engineer is reading is related to one of two potential real electrical distribution problems.

1. A missing neutral to ground bonding jumper at your friend's main service panel. If the bonding jumper is present and is properly connected, the neutral to ground voltage at the service panel will be extremmely low. This is the first test-> Check the N-G voltage at the service panel. If it is very low-> almost zero (it should be), then the problem is #2. If it's high get an licensed electrician to check the installation for compliance with the National Electrical Code, i.e., is the service neutral to ground bonding jumper properly installed?

2. Exessive voltage drop in the branch circuit/feeder feeding the elevator. Remember every circuit has impedance, i.e., both in the neutral and phase conductors as seen at the load. If he's measuring 3V to 3.5V neutral to ground it's quite likely that there's also a like voltage drop in the phase conductor, i.e., Kirchoff's law for voltage in a circuit. F. ex. if the supply at the service panel reads 120V phase to neutral and has extremely low neutral to ground voltage then the problem is quite likely the circuit impedance, i.e., he needs bigger circuit conductors to limit the circuit voltage drop.

When you measure the neutral to ground voltage at the load you are in reality measuring the neutral conductor voltage drop + the service neutral to ground voltage. The equipment grounding conductor of the circuit becomes a meter lead extension for your DVM, i.e., you are actually measuring across the neutral conductor. Solution -> install bigger circuit conductors.

So let's assume you have 120V phase to neutral from each phase at the service panel. If you have 3.5V N->G at the load , it's quite likely you will have 113V phase to neutral at the load, i.e., 3.5V drop in each conductor.

Neutral to ground voltage can be used as a pretty good indicator of the circuit volatge drop in a residential branch circuit. f. ex. 3.5V neutral to ground indicates a total voltage drop of ~ 7V. 7V/120V= ~6% Whereas, 2V neutral to ground indicates a total drop of ~4V. 4V/120V = 3%. The National Electrical Code recommends a maximum of 3% voltage drop for branch circuits.

Lastly- It would be helpfull to understand the physics of the circuit involved, i.e., what is the conductor size, conductor length (distance between the panel and the load), the circuit breaker size and the load amps.

Al

 

[itsmoked]

Nice response Al.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[edison123]

Al, I agree.

* I would go green if only I were not yellow *

 

[nasser214]

chek three phase current balance .try to balance currents.also chek if there is a heavy nonlinear load on branch.