Grounding at Service entrance

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bagunboy

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:smile: Sorry to jump in here but i have a question and I am a first time user. I cant find where to post a new question.
I live in the Caribbean and our Chief has switched to using the NEC. However he is asking for no more than 24 ohms at the service entrance is this a normal practice in the US. If so how do you guys achieve it normally
 
Grounding at Service entrance

I live in the caribbean and our Chief electrical engineer
(CEI) has recently switched to the NEC and is now asking for the 24 ohms or less at the service entrance. is this a normal practice in the US and if so how do you guys usually achieve this
 
The NEC does not require 25 ohms or less except for a single ground rod.

If the only service electrode is a single ground rod and you can not prove it has less than 25 Ohms resistance to earth then you add a second rod.

Once you add the second rod your done.
 
grounding at service entrance

grounding at service entrance

Well the same chief electrical engineer has warned that using two earth rods will not be reach the desired resistance. the challenge is when the inspector comes to site or residence he uses the meter if it not to the level he fails the job. the meters are just expensive here. I guess i will have to use about four rods then thanks guys. BTW do you guys have inspectors checking your jobs in order to connect to the pole.

bagunboy
 
See 2008 NEC 250.56 Resistance of Rod, Pipe, and Plate Electrode

The 25 Ohm requirement is for a single ground rod. Drive two seperate ground rods not less than six feet apart and that should take care of it. We have driven two ground rods for several years now.
 
I believe this is a duplicate thread. I am closing it. :grin:




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There is no basis for requiring 25-ohms or less of earth resistance for the service grounding electrode system on typical installations, which I assume you are refering to. Some of the telecom and/or power distribution guys may come in and explain why a low earth resistance is prefered for their systems, but most of your system of less than 600V will not require a significantly low earth resistance for proper operation.

I personally feel earth resistance testing or monitoring is a complete waste of time. As long as your services are grounded in compliance with Article 250 pf the NEC, no further evalutaion or concern should be given.

Depending on the conditions of the area you are in, it may be completely impractical or even impossible to acheive low earth resistances.
 
bagunboy said:
I live in the caribbean and our Chief electrical engineer
(CEI) has recently switched to the NEC and is now asking for the 24 ohms or less at the service entrance. is this a normal practice in the US and if so how do you guys usually achieve this
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Your "Chief" does not understand the purpose of a ground rod. At 120 volts, 24-ohms resistance on a ground rod will cause 5-amps of current. 100-ohms will only cause 1.2-amps of current. Who cares? Neither one will cause a fuse or breaker to trip. The main purpose of the ground rod is for high-voltage events such as a lightning strike or high-voltage lines coming into contact with secondary conductors. At 14,000 volts a 24-ohm resistance will result in 583 amps of current and 100 ohms would result in 140 amps, either of which will be plenty to trip a breaker or the fuse on the power company's primary. Buy your "Chief" Mike Holt's book on grounding and bonding.
 
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