Generator Neutrals

[hurk27]

Re: Generator Neutrals

ddderek You might have been shown diagrams that might show parallel paths on grounding system's when the system voltage is above 600 volts. MGN are multi grounded to Earth also. But it is the reason behind "why" that you must need to know. It as simple as ohms law. Take a made grounding electrode which just meets the required 25 ohm's if you take a hot conductor (120v to earth) by it self and connect it to this electrode how much current do you think will flow? only 4.8 amps. Now do this with a hot conductor that is 1kv to earth and now you have 40 amps flowing. This is the problem when mixing HV systems and low voltage systems. many of the diagrams will show extra grounding paths that are in parallel with the system neutral but some of these paths are acutely Earth which can not be used on a system that has 120 volts to earth. Now do you think this might be what you saw in those classes? as I cannot believe a electrical class would teach it's students something that not only is a direct violation of the NEC but has the potential to cause injury and or death if someone were to touch a conduit that has current running through it if the path through it was disrupted?
If you have the name of the book that we can get to confirm what you say. It would let us all learn. Or let us know that there is still some miss-informed book writers out there that maybe needs to be corrected. Before someone get's hurt by this bad information. I'm not saying your are wrong just miss-informed.

[ February 14, 2005, 07:27 PM: Message edited by: hurk27 ]

 

[ddderek]

Re: Generator Neutrals

Originally posted by hurk27:
If you have the name of the book that we can get to confirm what you say. It would let us all learn.

It was part of the code update class for the 2002 code... Called "analysis of changes in the 2002 NEC" Just as they are offering this for the 2005 now... Here in Michigan we are just getting up to the 2002 for next years licenses.

And who can I contact at a NEC facility to ask for more regulation and clarity of generator issues for future code books. I understand Canada has it spelled out very clear and they offer three pole transfer switches for that reason. You can NOT buy one in the USA for manually switching the two phase conductors and the neutral. I tried to purchase the Siemans one from Canada but it is not UL listed and no dealer here could get one for me that was...

 

[crossman]

Re: Generator Neutrals

I will chime in and say again... the major danger with a neutral bond on the load side of the service arises when the neutral connections become less than ideal, leaving the majority of the current and voltage across the EGCs which may be conduit, enclosures, etc.

Remember the parallel conductor thread where we cut one of the conductors? My point was to apply the theory to a neutral bonded on the load side of the service.

With a multiple bonded neutral in parallel with the EGCs, certainly some of the current will flow on the EGCs. But unless the neutral itself becomes high impedance from bad connections or is broken or disconnected, there is no real danger to personnel or property. Certainly there will be some Electromagnetic flux that doesn't get cancelled. But if the neutral itself is compromised, then VERY BAD THINGS can happen, and this in itself is reason enough for the practice to not be allowed by the NEC... and it is most certainly not allowed.

There are literally hundreds of thousands of installations where the subpanel neutrals are bonded, etc. For the most part, these are "safe" installations as evidenced by the fact that they have been up and running for decades. But all it takes is a loose or corroded neutral connection and then the potential for disaster is there. Again, reason enough to not permit the practice.

Don't bond the neutral on the load side of the service!!!!!!!

(all of the above is my opinion)

 

[hurk27]

Re: Generator Neutrals

We also must keep this in mind what Tom posted earlier:

conduit fittings are not designed to carry current all the time (only in a fault) the fitting will heat and cause a fire. Remember the MGM Grand Fire in 1984? many people died from a fire due a loose electrical fitting.

 

[Ed MacLaren]

Re: Generator Neutrals

You can NOT buy one in the USA for manually switching the two phase conductors and the neutral.

Try your local Square D products dealer.
Below is a clip from the Square D calalog. I have used the #92351 often for residential jobs.

Ed

 

[ddderek]

Re: Generator Neutrals

Try your local Square D products dealer.
Below is a clip from the Square D calalog. I have used the #92351 often for residential jobs.

Ed

Explain to me where you put that switch Ed and how it would work... That is a 30A D.T. switch and I don't see how it would work other than as a whole servce disconnect but 30A would not be large enough.

[ February 15, 2005, 10:12 AM: Message edited by: ddderek ]

 

[Ed MacLaren]

Re: Generator Neutrals

Explain to me where you put that switch Ed and how it would work...

This was discussed in this very thread back on Jan 16th and 17th-2005. See page 2.

I can post diagrams showing the actual connections if you wish.

Ed

 

[ddderek]

Re: Generator Neutrals

What about this situation?

Service comes from Meter to 200A 3P Fused Disconnect,

At disconnect, 3rd pole is used for neutral, Meter neutral to top, neutral to house on bottom, and top lug is double lug that goes to grounding for neutral bond for service.

At inside panel, 200A main breaker is interlocked with two pole breaker for Gen back up.

Under Gen power situations, using bonded neutral Gen, you throw the outside disconnect off, breaking neutral bond to ground, use panel interlock for phase conductors. Have you then seperated the bonding sufficiently to satisfy code.

OR is the fact that the Utility Neutral is still connected to the ground outside, still a violation?

A 200A D.T. switch is $2000 that is what I am trying to avoid purchasing along with the $800 WP 200A Disconnect...

 

[ddderek]

Re: Generator Neutrals

This was discussed in this very thread back on Jan 16th and 17th-2005. See page 2.

I can post diagrams showing the actual connections if you wish.

Ed

Thanks Ed I see and remember it now... the reason that would not work for what I want to do is that I am trying to configure so that ANY circuit can be used not just a few selected ones. What do you think about my other scenario?

 

[rbalex]

Re: Generator Neutrals

Originally posted by ddderek:
?
And who can I contact at a NEC facility to ask for more regulation and clarity of generator issues for future code books...

The basic way the NEC (or any other NFPA Standard) gets changed it through formal public proposals to change it. This forum has been created to assist folks that wish to make a formal Proposal. Be sure to read the ?Welcome.? Also check this web page for more information about the NFPA Code Making Process.

Occasionally, a Technical Committee (TC) or Code Making Panel (CMP) may make its own proposal or respond to directions from a Technical Correlating Committee (TCC) or the Standards Council (SC). Under the current rules, neither the SC nor a TCC may actually write code although they may reject the work of a TC. The NFPA Staff has no direct authority to write, change or reject anything; they are nevertheless the real workhorses of the process, extremely knowledgeable and highly influential.

 

[Ed MacLaren]

Re: Generator Neutrals

What do you think about my other scenario?

If I understand your description correctly, it would resemble the sketch below.
It's OK only for generators with the neutral not bonded to the frame.

Under Gen power situations, using bonded neutral Gen, you throw the outside disconnect off, breaking neutral bond to ground,

How would that break the "neutral bond to ground"?

OR is the fact that the Utility Neutral is still connected to the ground outside, still a violation?

The neutral that is being used by the load circuits is required to be earth grounded, no matter which source is supplying them.

Ed

[ February 15, 2005, 02:00 PM: Message edited by: Ed MacLaren ]

 

[ddderek]

Re: Generator Neutrals

Not exactly Ed,
I was speaking about using a THREE pole fused disconnect and on the line side connecting the utility neutral and main bonding jumper in a double lug. THEN on the load side would be the neutral to the inside panel. HENCE turning off the disconnect switch would remove the bond from the panel feed neutral to ground. HOWEVER the utility neutral would still be connected to ground. AND of course this would be using a Gen with a bonded neutral? Does this accomplish what I am trying to or is the fact that that utility neutral still connected to the ground system cancel out what I am trying to do by isolating the neutral feeding the panel?

 

[hurk27]

Re: Generator Neutrals

ddderek
Do you understand the danger of having a "fuse in the neutral conductor?

230.90 (B) Not in Grounded Conductor. No overcurrent device shall be inserted in a grounded service conductor except a circuit breaker that simultaneously opens all conductors of the circuit.

If you ever have that fuse open you will have alot of damage equipment or even a fire.

 

[ddderek]

Re: Generator Neutrals

Originally posted by hurk27:
ddderek
Do you understand the danger of having a "fuse in the neutral conductor?

230.90 (B) Not in Grounded Conductor. No overcurrent device shall be inserted in a grounded service conductor except a circuit breaker that simultaneously opens all conductors of the circuit.

If you ever have that fuse open you will have alot of damage equipment or even a fire.

Thanks, I was unaware of that and didn't stop to think about it but it sure makes sense... so that is definitely an unacceptable method... I guess the only answer is the $2000 200A 3pole Double throw disconnect switch or make sure the generator has an isolated neutral whether I isolate or it comes that way...

[ February 16, 2005, 07:31 AM: Message edited by: ddderek ]

 

[ddderek]

Re: Generator Neutrals

OK a little help here.... anyone who has the 2005 code and can look at these sections to verify for me.... read the following thread to understand what I am talking aboput to this manufacturer that has a grounded neutral on all ends for gen hook ups... Just read...

21 Feb 2005

Attn: Derek

If you look at the current National Electric Code
2005, not the 2002 code, which has been in effect
since August 5, 2004, please note the following
sections:
250.20, 250.24, 250.26, 250.32, 250.188 and 250.190.
There is additional information throughout the
grounding regulations. Kinldy note that our owner's
manual state "Any home wiring modification or the
installation of a manual transfer switch and out door
connection box must be done by a qualified and
licensed electrician. He must be sure that the
installation meets all applicable local and national
codes. NOTE: Any permanent installation must comply
with the National Electrical Code, and all local and
state codes"

We will continue to ground all neutrals.

Regards,
SML Industries, Inc.
--- Original Message ---
From: "Derek" <ddderek@twmi.rr.com>
To: <SMLSALES@flash.net>
Subject: Re: Generator questions

>So you are not going to address this issue? I will
forward your owners
>manual to the appropriate licensing authorities...
if you continue to ignore
>the safety violation that you are showing consumers
how to install. (you
>said the NEC requires a bonded neutral... YES... BUT
only at one location!
>You are instructing the consumers leave it bonded in
two locations or on the
>load side of the service disconnecting means. A
clear violation and safety
>issue)
>
>Thank YOU...
>
>----- Original Message -----
>From: <SMLSALES@flash.net>
>To: "Derek" <ddderek@twmi.rr.com>
>Sent: Saturday, February 19, 2005 5:04 PM
>Subject: Re: Generator questions
>
>
>> 19 Feb 2005
>>
>> Thank you.
>>
>> --- Original Message ---
>> From: "Derek" <ddderek@twmi.rr.com>
>> To: <SMLSALES@flash.net>
>> Subject: Re: Generator questions
>>
>>>Actually your owners manual is mistaken when it
>> requires a 2 pole transfer
>>>switch... It is illegal for the neutral to be
>> grounded on the load side of
>>>the service disconnect which would be the
generator.
>> Refer to 2002 NEC
>>>250.24(5) which refers you to 250.30 (1) exception
>> no. 1 says that the
>>>bonding will only be allowed if it does not create
a
>> parallel path. This is
>>>exactly what your recommended hook up does....
>> Bonded at the service and at
>>>the Generator create a parallel path for return
>> current to the gen.
>>>Providing a hazard upon loosing the neutral bond at
>> the gen because current
>>>would travel on the ground and frame would be
>> energized. I have had this
>>>converstion with inspectors that wrote the NEC and
>> you are in violation of
>>>the NEC with the instructions in your owners
manual.
>>>
>>>I would appreciate your further feedback.
>>>
>>>-Derek
>>>----- Original Message -----
>>>From: <SMLSALES@flash.net>
>>>To: "Derek" <ddderek@twmi.rr.com>
>>>Sent: Friday, February 18, 2005 6:03 PM
>>>Subject: Re: Generator questions
>>>
>>>
>>>> 18 Feb 2005
>>>>
>>>> Attn: Derek
>>>>
>>>> The National Electric Code, the Canadian Electric
>>>> Code and practically all local codes require a
>>>> grounded neutral. We are complying to these
codes
>>>> and will not change our owner's manual as we must
>>>> comply with the current codes. In selected other
>>>> parts of the world, Germany etc, a floating, not
>>>> grounded neutral, is the local code.
>>>>
>>>> In connecting a portable generator to a home or
>>>> building through a double pole, double throw
>> switch,
>>>> you bring in two lines(hot wires) a neutral and a
>>>> ground wire. As we ground the neutral, you think
>> you
>>>> only need to bring in three wires but the codes
>>>> require 4 wires in case you internally loose the
>>>> grounded neutral inside the generator.
>>>>
>>>> Regards,
>>>> SML
>>>>
>>>> --- Original Message ---
>>>> From: "Derek" <ddderek@twmi.rr.com>
>>>> To: <smlsales@flash.net>
>>>> Subject: Generator questions
>>>>
>>>>>Generator Owner's Manual (pdf)
>>>>>A25 Series, A30 Series, A50 Series, A60 Series,
>>>> LA50/55 Series, LA60 =
>>>>>Series, LR70/80/105 Series
>>>>>
>>>>>In the forementioned owners manual you show
proper
>>>> hook up being a =
>>>>>2-pole transfer switch for your generator models.
>>>> Then the wiring =
>>>>>diagram goes on to show that the generator has a
>>>> bonded neutral system. =
>>>>>That combination appears to be in violation of
the
>>>> National Electric =
>>>>>Code? Could you please elaborate on your side of
>>>> this and if indeed it =
>>>>>is will you be altering your owners manuals for
the
>>>> future?
>>>>>
>>>>>Thank you in advance for your assistance.
>>>>>
>>>>>-Derek

 

[Ed MacLaren]

Re: Generator Neutrals

derek,
Very interesting. The sad truth is that some of the generator manufacturers are not up to speed on this.

Here is a link to an application note on the Schneider/Square D website.

The diagrams are a little hard to follow, (not as good as mine ) but the text explains the requirements clearly.

The code references are for the Canadian code but the rules are the same as the NEC in their effect.

Generator/Transfer Switch Connections

Hope this helps,
Ed