Having 2 Generators

[groundedroger]

Background:

A client was using 2 portable generators in the past; a Generac 5KW and a Yamaha 2.4 KW Inverter for their home office. They were not operating in parallel, they were used using separate cables feeding the appliances, lights, while the inverter was eeding the home office UPS's which were connected to their pc's, router, cable box/modem, FIOS Phone/Internet. Everything was working fine.

They decided to go with a 30 AMP interlock system using the 5 KW generator, which I installed and tested out.

During testing, their UPS's would trigger, as was expected, during appliance power surges, and even during printer active job surges.
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The question is, can they also use their inverter to power their home office:

The home office has a completely isolated (from house power) electrical feed cable, which was used originally when they were using the 2 generators.

All they want to do is connect the inverter to their 5 UPS's. These UPS's power 3 computers, cable modem/gigabit sw, FIOS modem/gigabit sw, and one printer which is connected to the surge protector side.

Initially everything seemed fine to me, and even the inspector did not have an issue when I asked.

But as I thought about it more,

They have another 3 cable modems in the house, which will be powered by the other generator. They also have other computers in the house, using CAT5 cables, which will be powered by the inverter generator.

SO here is the BIG Question:

Can we do this? Is there a code covering this:
even though the electrical circuits are completely isolated, there are secondary connections through the RF/video/CAT5 conenctions.

BTW: The cable and FIOS are grounded to the house water pipe, as is the main power. The 5 KW generator is left bonded; it is not grounded using additional means.

 

[Martin B]

For the cost of two small generators and installation couldn't you just install one larger generator (like a 10 or 15kw) and automatic transfer switch and back up the whole house??? Some automatic transfer switches come with load shedding relays so you could drop a appliance or two if necessary.

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[tkb]

This not something that should be DIY.
Call an electrician.

 

[groundedroger]

For the cost of two small generators and installation couldn't you just install one larger generator (like a 10 or 15kw) and automatic transfer switch and back up the whole house??? Some automatic transfer switches come with load shedding relays so you could drop a appliance or two if necessary.

Sent from my LGUS610 using Tapatalk

It is not a question of larger generator, as their 5 KW can handle the home office too. It's about getting improved quality on the 60 HZ frequency and minimum voltage variation using the inverter. The Yamaha Inverter costs a lot more than the 5 KW Generac, so adding a second inverter in parallel is too costly.


The question really comes down to an we have CAT5 & coax cables connecting to computers, switches fed from 2 different power sources.

I do not think this is covered anywhere, or I may have missed it.
Everyone I asked so far told me they are not sure.

 

[Martin B]

After posting I started thinking the same thing. I agree with tkb

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[groundedroger]

Not sure

Not sure

This not something that should be DIY.
Call an electrician.

I asked 2 electricians and an inspector and they were not sure.

 

[Martin B]

It is not a question of larger generator, as their 5 KW can handle the home office too. It's about getting improved quality on the 60 HZ frequency and minimum voltage variation using the inverter. The Yamaha Inverter costs a lot more than the 5 KW Generac, so adding a second inverter in parallel is too costly.


The question really comes down to an we have CAT5 & coax cables connecting to computers, switches fed from 2 different power sources.

I do not think this is covered anywhere, or I may have missed it.
Everyone I asked so far told me they are not sure.

I am confused why "your customer" is insisting on having two power sources. The UPS would protect the sensitive electronics.

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[publicgood]

Having 2 Generators

I asked 2 electricians and an inspector and they were not sure.

The inspector and electricians are responding based on their level of compensation and liability. You need a qualified electrician with design abilities matching the scope of work. The permitting process may even require a licensed professional engineer to stamp drawings.

Among other things: grounding/bonding, service disconnects, backfeeding, NFPA 37, etc. are all applicable to your installation. Those are just related to code and safety, not to mention operational considerations of the unknown capacity of the noted UPSs, power factor on the system, etc.

There is not nearly enough information to assist you. DIY is not covered in this forum.

 

[JFletcher]

One potential problem is that you have a common ground (via the coax shield) connecting different electronics powered by different power sources. Normally all of those devices are grounded and bonded thru the shield via the first CATV splitter which is grounded back to the service. Having two generators (and basically two services) could cause problems if the grounds of the generators are not at the same potential relative to each other and to earth.

Cat5e cable doesn't have a ground wire or pair.

For codes regarding the coax and phone lines, look up 800.100, 820.100 for starters.

I am not sure what codes come into play in running two generators (and UPS?) together, especially when it's impossible to operate them in synchronicity (parallel). publicgood brought up other key issues with your install.

eta: I would be looking at a larger, single generator, or reducing loads so that one is sufficient. The 2.4kW generator alone is 20A @ 120V; I've a hard time believing the essentials of a "home office" with a modem, router, computer, etc. would come close to taxing that.

How often do the generators run?

 

[hbiss]

They decided to go with a 30 AMP interlock system using the 5 KW generator, which I installed and tested out.

So now EEs and computer programmers do electrical work?

-Hal

 

[groundedroger]

The coax ground is my concern too!

The coax ground is my concern too!

Even though everything else is completely isolated, the coax GND connection at the first splitter to the water pipe will be an issue.

The reason this set up of using 2 generators has worked for 10 + years was that they were bypassing the breaker box; not grounded to the house ground. They were all independent devices.

Even though the CAT5 do not have a ground in the cable, the network card may still have issues because it is connected to the motherboard which is chassis ground.

I developed a simple diagram so everyone can have a visual. The RED lines are the "Potential Issues"!!

 

[groundedroger]

Load

Load

One potential problem is that you have a common ground (via the coax shield) connecting different electronics powered by different power sources. Normally all of those devices are grounded and bonded thru the shield via the first CATV splitter which is grounded back to the service. Having two generators (and basically two services) could cause problems if the grounds of the generators are not at the same potential relative to each other and to earth.

Cat5e cable doesn't have a ground wire or pair.

For codes regarding the coax and phone lines, look up 800.100, 820.100 for starters.

I am not sure what codes come into play in running two generators (and UPS?) together, especially when it's impossible to operate them in synchronicity (parallel). publicgood brought up other key issues with your install.

eta: I would be looking at a larger, single generator, or reducing loads so that one is sufficient. The 2.4kW generator alone is 20A @ 120V; I've a hard time believing the essentials of a "home office" with a modem, router, computer, etc. would come close to taxing that.

How often do the generators run?

The steady state load applied to the inverter is only 15 A. They are cloud based, so there is no Server involved.

To reiterate, it's the quality of the AC signal (when viewed on a scope), produced by the inverter vs, the regular generator. Once it stabilizes after 1 minute, then it is close to utility power quality in frequency and peak amplitude.

 

[JFletcher]

The steady state load applied to the inverter is only 15 A. They are cloud based, so there is no Server involved.

I have no idea what that means in the context of this topic.

I understand that the 5kW Generac probably doesnt have a clean or nearly sinusoidal enough output to satisfactorily operate sensitive electronics.

The "secondary" connection between the generators and equipment existed before you installed the transfer switch, and went thru the panel and water pipe ground. That you are now going thru the panel with one generator is irrelevant in that regard: as I previously wrote, all of the equipment with CATV was connected together via the outer shield/braids/ground of the cable.

All TVs with a cable connection and the modem are all electrically connected to each other via the shield of the coax. The connection of that first splitter to the water line and to the panel eventually bonds the whole thing to the service neutral... but do not assume you have that connection. Older installs, here anyway, the cable co pounded a 5' ground rod at the NID and ran a #14 copper from it to the splitter, never going back to the service.

Re: the potential problems with the coax, power isolators can be used to prevent ground loops:

http://www.21best.com/21_best/electronic/security/video/filters/CATV-ISOLATOR/Outline.jpg

Modems, routers, computers and printers are all user equipment and outside the scope of the NEC.

What kind of PoE camera also requires line (120V) voltage?

Does that Yamaha inverter generator have a floating neutral?

 

[publicgood]

The steady state load applied to the inverter is only 15 A. They are cloud based, so there is no Server involved.

To reiterate, it's the quality of the AC signal (when viewed on a scope), produced by the inverter vs, the regular generator. Once it stabilizes after 1 minute, then it is close to utility power quality in frequency and peak amplitude.

It isn't just about steady state. Batteries on the UPS needs to be charged too, unless it is simple line interactive capacitor based.

If the concern is quality, even if (2) AC sources, you have not provided any details about the UPS. If it is not online double conversion, your subject to the input source. Generators, even in the MW range, are not considered similar power quality. Not in terms IEEE will define at least if we are using scopes. The sub-transient reactance drives ability to accept harmonic content. With the gens and UPSs possibly sized close the perfect sine wave is unlikely.

Further more if the concern is quality additional sources do not provide this. They only provide reliability during loss of source and concurrent maintainability.

If the UPS is serving 120V loads, there is a shared neutral between sources.

 

[groundedroger]

I have no idea what that means in the context of this topic.

I understand that the 5kW Generac probably doesnt have a clean or nearly sinusoidal enough output to satisfactorily operate sensitive electronics.

The "secondary" connection between the generators and equipment existed before you installed the transfer switch, and went thru the panel and water pipe ground. That you are now going thru the panel with one generator is irrelevant in that regard: as I previously wrote, all of the equipment with CATV was connected together via the outer shield/braids/ground of the cable.

All TVs with a cable connection and the modem are all electrically connected to each other via the shield of the coax. The connection of that first splitter to the water line and to the panel eventually bonds the whole thing to the service neutral... but do not assume you have that connection. Older installs, here anyway, the cable co pounded a 5' ground rod at the NID and ran a #14 copper from it to the splitter, never going back to the service.

Re: the potential problems with the coax, power isolators can be used to prevent ground loops:

http://www.21best.com/21_best/electronic/security/video/filters/CATV-ISOLATOR/Outline.jpg

Modems, routers, computers and printers are all user equipment and outside the scope of the NEC.

What kind of PoE camera also requires line (120V) voltage?

Does that Yamaha inverter generator have a floating neutral?

I meant that they are only loading the inverter to about 75% load capacity.

Cloud based meant that they are only using low power consumption workstations, instead of power hungry servers. Their old server consumed 7 Amps!

Even though the main generator can supply the entire house (minus air-conditioners) using a 30 AMP interlock breaker, they just wanted to use the inverter too as they did before for cleaner AC.

The POE cameras I installed do not carry 120 VAC, instead the standard POE voltage, which is about 44 VDC. The POE gigabit switches provide this power.

The cable ground connection was not good when I checked it; it used to go to an un-used disconnected outdoor metallic conduit, which was next to the cable splitter. I called the cable company and they connected it to the water pipe. I did not like the fact that the cable guy just connected it to the outdoor pipe because it was 6 feet away, instead of wiring it inside, at the same spot the main ground is connected to. I may run the wire myself and call them to inspect it. The way they wired it can cause ground loop, or loose ground all together if they decide to cut the outdoor spigot in the future!

I think the inverter has a floating ground, but I did not check it. I will in the future. It's the Yamaha 2400.

 

[groundedroger]

UPS

UPS

They are standard APC 1500 VA UPS units. Hey have 5 of these, powering the network gear, poe swtches, routers, pc's.

 

[groundedroger]

I was surprised that this has not come up before to the people I asked. These were all licensed/certified people, including a town inspector.

They were not considering the secondary affects of the RF coax ground.

I am considering workarounds....in using the inverter generator, otherwise I would recommend keeping it in the event the main dies during a power outage. These can be put in parallel mode but they are costly. Two of these in parallel can power the house.They are ultra quiet and they do not consume too much gasoline. But I like simplicity when it comes to generators, and having a parallel connection is not something I like to do. I am the Keep it Simple type of a guy.

 

[charlie b]

I am going to put a temporary halt to this thread, and ask groundedroger to send me a private message. What I need to know is your involvement in this project. It appears to several of us that you are acting in the role of a do-it-yourself electrician. So please let me know:

• In what sense is the owner of this facility a “client”?
• Your profile says you have a BSEE, but also says you work in computer programming. Are you being paid by the client to perform design work on an electrical system?

The forum owner does not permit the forum members to assist an engineer in the design, installation, or troubleshooting of electrical systems that are not part of that person’s job responsibilities. If that does not apply to you or to this thread, then please explain in a PM.