Siemens Interlock Switch

[schildi]

Hi everybody!
I want to wire up a portable generator, and have a few questions:
- the load center is a Siemens G3040MB1200. Can anybody here help me with the selection of the correct Siemens Manual Interlock Switch part number?
- which breaker should I use for the generator (5,000W)? 40A two pole?

Any help is very much appreciated.
Thanks,
Mike.

 

[Smart $]

Hi everybody!
I want to wire up a portable generator, and have a few questions:
- the load center is a Siemens G3040MB1200. Can anybody here help me with the selection of the correct Siemens Manual Interlock Switch part number?
- which breaker should I use for the generator (5,000W)? 40A two pole?

Any help is very much appreciated.
Thanks,
Mike.

My best guess would be an ECSBPK03 matching with a G3040B1200 load center from this catalog excerpt...

http://cmsapps.sea.siemens.com/controls/speedfax07/07Speedfax_pdfs/07Speedfax_17/17_09-10.pdf


As to the panel breaker for gennie feed, I'd go same to one size larger than the breaker on the gennie

 

[K8MHZ]

How are you going to prevent the neutral and the ground coming from the generator from being paralleled?

Portable genny's have the neutral and ground bonded at the generator. When connected to the panel there will be another bond point. This will cause a good portion of the current meant to flow on the neutral to flow on the grounding conductor back to the generator.

 

[iwire]

Portable genny's have the neutral and ground bonded at the generator.

I do not think that is a standard, my 5000 watt Coleman is clearly labeled "Floating Neutral"

 

[schildi]

How are you going to prevent the neutral and the ground coming from the generator from being paralleled?

Portable genny's have the neutral and ground bonded at the generator. When connected to the panel there will be another bond point. This will cause a good portion of the current meant to flow on the neutral to flow on the grounding conductor back to the generator.

Is that a major issue? As long as the combined wire can support the current ...?

 

[Smart $]

I do not think that is a standard, my 5000 watt Coleman is clearly labeled "Floating Neutral"

I don't know whether there is a standard. Mine is bonded...

2.4.1 SYSTEM GROUND
The generator has a system ground that connects the generator frame components to the ground terminals on the AC output receptacles. The system ground is bonded to the AC neutral wire in the generator control panel via a jumper wire.

 

[acrwc10]

I do not think that is a standard, my 5000 watt Coleman is clearly labeled "Floating Neutral"

Just curious, is this a portable generator, built in receptacles, or is this a stand by for the house ? Because if it is portable and has a floating neutral how would the ground work, because it wouldn't be connected to a return path?
I would guess if there is one 4 wire receptacle only, for connection to a house, then the neutral would be floating. If on the other hand, there is a multiple receptacle set up, 120 3 wire, 120/240 4 wire, etc., the neutral would be bonded inside the generator.

 

[iwire]

is this a portable generator, built in receptacles, or is this a stand by for the house ? Because if it is portable and has a floating neutral how would the ground work, because it wouldn't be connected to a return path?

Portable with a pair 5-20Rs and a L14-30R.

The ground would not do anything except keep the item generators frame at the same potential as the EGC plugged into it.

 

[K8MHZ]

I don't know whether there is a standard. Mine is bonded...

All the one's I just saw at HD were clearly labeled as bonded.

 

[schildi]

All the one's I just saw at HD were clearly labeled as bonded.

So does it really matter? What is the potential problem?

 

[Smart $]

Portable with a pair 5-20Rs and a L14-30R.

The ground would not do anything except keep the item generators frame at the same potential as the EGC plugged into it.

Are you sure the neutral is not bonded to the EGC and frame?

With the neutral bonded to the frame and grounding terminals, the generator would still have a floating neutral. Only when it is connected to an earth grounded system or a grounding electrode does it not have a floating neutral.

 

[Smart $]

So does it really matter? What is the potential problem?

Every one screams hazard, but in reality (IMO) there is little to be concerned with. While it may create a parallel neutral path, the grounding conductor of connecting cord is (should be) insulated, and the exposed parts of the gennie are at the same potential as the neutral. What's the big deal I have to ask?

 

[K8MHZ]

I do not think that is a standard, my 5000 watt Coleman is clearly labeled "Floating Neutral"

Quite a discussion on it here:

http://ths.gardenweb.com/forums/load/wiring/msg1223360510195.html

And here, http://members.rennlist.org/warren/genfaq.html which says:

Using a generator with bonded neutral and ground in a system which does not switch neutral in the main panel leads to a potential safety issue. Neutral and ground will be connected at both ends of the extension cord, thus making them one conductor.

How is it possible to switch the neutral while using an interlock switch to backfeed an entire panel? The only place to put a switch would be from the genny which does absolutely nothing, as it needs to be closed when the genny is running.

The way I see it is that if you are going to backfeed an entire service panel, you need a generator with no bond as that would mean two. Where it gets dicey is that the rules say the bond has to be at the first disconnect, which would mean at the generator.

If you are going to feed a separate panel using a portable generator with on board OCPD, then the bond is made at the genny and not in the panel, and the neutrals are switched in a manner that disconnects them from the AC mains while the genny is being used. Easy to do, life is good, makes sense and satisfies the rules.

Those interlocks are cool, but if you think it through, is there really a way to use them and satisfy all the rules?

 

[hillbilly1]

Some portables have built in ground fault protection, which causes problems when the ground and neutral are connected together on the load side. My uncle had a Honda which he used to run a picnic shelter and cabin, the generator was remotely located away from the buildings, and supplied power via a two wire service drop 50' away. This had been the case since the late 60's, when he replaced the old generator with the new one, the GF would not hold. I had to bypass it, as the entire system would have to be replaced, fuse panel and all to work with the new generator.

 

[K8MHZ]

Are you sure the neutral is not bonded to the EGC and frame?

With the neutral bonded to the frame and grounding terminals, the generator would still have a floating neutral. Only when it is connected to an earth grounded system or a grounding electrode does it not have a floating neutral.

On another site discussing these generators one of the posters there said he verified the lack of bonding with a meter.

 

[K8MHZ]

Every one screams hazard, but in reality (IMO) there is little to be concerned with. While it may create a parallel neutral path, the grounding conductor of connecting cord is (should be) insulated, and the exposed parts of the gennie are at the same potential as the neutral. What's the big deal I have to ask?

I'm not screaming hazard. I am pointing out the rules. FWIW, we are talking about what the NEC deems 'objectionable current'. Like most that have just been unceremoniously left without power, I wouldn't object to any current on the EGC that it was sized for. My concerns would be having enough power to run what is needed at the time.

But the NEC has made it pretty clear that intentional load current on the EGC is not allowed. They indeed object. So I guess it boils down to who gets to be the one to object or not....

 

[Smart $]

Some portables have built in ground fault protection, which causes problems when the ground and neutral are connected together on the load side. My uncle had a Honda which he used to run a picnic shelter and cabin, the generator was remotely located away from the buildings, and supplied power via a two wire service drop 50' away. This had been the case since the late 60's, when he replaced the old generator with the new one, the GF would not hold. I had to bypass it, as the entire system would have to be replaced, fuse panel and all to work with the new generator.

Not sure how you bypassed it, but all you should have done is remove the N-G bonding jumper on/in the gennie, as there was a main bonding jumper elsewhere.

 

[Smart $]

I'm not screaming hazard. I am pointing out the rules. FWIW, we are talking about what the NEC deems 'objectionable current'. Like most that have just been unceremoniously left without power, I wouldn't object to any current on the EGC that it was sized for. My concerns would be having enough power to run what is needed at the time.

But the NEC has made it pretty clear that intentional load current on the EGC is not allowed. They indeed object. So I guess it boils down to who gets to be the one to object or not....

Just where does the NEC make that pretty clear?

 

[K8MHZ]

Just where does the NEC make that pretty clear?

To me it's clear.

For example, we are now going to be required to bring neutrals into switch boxes because some devices have been using the EGC as a means to carry just a tiny bit of current to operate them.

They are clear about a single point of connection between the neutral and the ground, are they not?



Where is it not clear to you?

 

[hillbilly1]

Not sure how you bypassed it, but all you should have done is remove the N-G bonding jumper on/in the gennie, as there was a main bonding jumper elsewhere.

This particular model used a powered groundfault protection system that utilized an external CT and a shunt trip breaker, removed power to the control module. Since the old wiring was only a two wire drop, it contained only a unisulated neutral, and a insulated hot. Removing the N-G jumper would not solve the problem because a fault to ground on the load side at the generator would cause a potential between the frame and the earth, for ground fault protection to work properly, the bond must be on the line side of the ground fault device.