# Daisy Chain Service Entrance?



## Frasbee (Apr 7, 2008)

We got skadude, and rudeboy on the boards.

I see a skank pit in the near future.


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## oldtimer (Jun 10, 2010)

skadude said:


> I'm trying to install a wind turbine to this location. I have a variety of ideas how to connect, I just want to do the cheapest, as this is for a rural school district.
> 
> Already checked current ratings on everything, and they seem good. Turbine inverter voltage is 120/240V Split Phase. I will install a fused knife-blade switch box next to existing box for the wind turbine, then buried cable to another box at turbine site. My question is, can I wire the line-side of the switch into the line-side lugs on the existing breakers? Please indicate code reference. Below is a link to some pictures of the site.
> 
> ...


 You will have to install a transfer switch. A must I M O, preferably an A T S.


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## Bob Badger (Apr 19, 2009)

oldtimer said:


> You will have to install a transfer switch. A must I M O, preferably an A T S.


I am guessing here that he is using a listed grid tied inverter that back feeds into the utility. No transfer needed.

However ..... if it is grid tied his first stop should be the power companies web site and look for their interconnection agreement for all the rules. 

It will be about 100 type written pages. :laughing:


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## kub (May 27, 2009)

whats the info on the turbine? Is the inverter built in or separate? if grid-tied you'll need a meter in there somewhere to determine how much power it has produced for the poco to read.


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## MDShunk (Jan 7, 2007)

kub said:


> whats the info on the turbine? Is the inverter built in or separate? if grid-tied you'll need a meter in there somewhere to determine how much power it has produced for the poco to read.


Not necessarily. Every utility does it different. If they're buying it back at rate, some will just let you run the present meter backwards.


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## skadude (Aug 3, 2010)

Wind Turbine is Skystream 3.7 by Southwest Windpower. The inverter is built-in and all UL certified. No need for transfer switch, utility just requires disconnect switch they can access if they feel the need, which I include anyway. Metering is done via bi-directional meter.

With the age of the equipment and the current configuration, I may need to replace everything, but wasn't sure if I could just wire the turbine disconnect directly into the line-side lugs of the existing breakers.


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## Introyble (Jul 10, 2010)

I have no experience with this topic so I'm trying to learn by answering your question. Somebody correct me if I am wrong.

Read NEC 690

There must be appropriate first to make/last to break circuit over current protection (in accordance with article 240) between the inverter output and all conductors. This point must be labeled with inverter operating AC voltage and rated AC output current. This utility disconnect must also be labeled with a warning label against connecting branch circuits at this point.

Further, 690 states no multiwire brance circuits are allowed on 120V inverter output circuit or panels. 

You are allowed to connect up to six disconnects from a single inverter power souce. These disconnects can not be rated for more than 125% of the maximum current rating of the inverter.

Keep in mind the largest single load on the system may not exceed the stated maximum ouput rating of the inverter. However, the sum of all the loads on the system may exceed the maximum inverter output ratings.

For the sake of argument, you are allowed to multi tap directly off the secondary side of a transformer. If secondary protection isn't required for the transformer, then running multiple feeder taps from that secondary becomes possible. We think there is no limit to the number of such taps, as long as each feeder tap meets all the rules in Sec. 240-21(m):

(m) Outside Feeder Taps. Outside conductors shall be permitted to be tapped to a feeder or to be connected at the transformer secondary, without overcurrent protection at the tap or connection, where all the following conditions are met:

Following this, there are five conditions all of which we will stipulate to have been met in this case. In the drawing, each feeder has been connected at the transformer secondary, and we will assume adequate protection from physical damage (condition 1). The feeders run outdoors (condition 3) and terminate at a single disconnecting means and suitably sized overcurrent device (conditions 2, 4 and 5), as previously noted. There is no language in any of the conditions that prevents multiple feeder connections. The "conductors" referred to in the various conditions and the "single" overcurrent device are the conductors and the associated overcurrent device that comprise the feeder and its protection to a given building; a second feeder involves a different group of conductors and a different overcurrent device. As long as the transformer protection meets Code requirements, and each feeder tap has the prescribed protection, multiple feeders can be connected.

Remember, this tap rule, although seldom used in this way, also applies to taps from a large outdoor feeder.


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## skadude (Aug 3, 2010)

Introyble,

I appreciate your thoughts. I would like to question one of your statements:



Introyble said:


> You are allowed to connect up to six disconnects from a single inverter power source. These disconnects can not be rated for more than 125% of the maximum current rating of the inverter.


This statement seems to conflict with NEC 230.79, part D. I, and others I have worked with, have interpreted any inverter connecting to the line-side of an existing system to only be classified as in part D, thereby requiring a service disconnecting means of no less than 60 A.

By the way, the maximum sustained current of the wind turbine's inverter is 20A.


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## Introyble (Jul 10, 2010)

The way I worded it didn't make sense, I won't argue. 



690.14(C)(4 -5) There are to be no more than 6 D/C's grouped togther.

690.8(b) overcurrent protection devices are rated for not less than 125% of the maximum currents calculated or determined by 690.8(A)

before we read 690.8(a) let me point out that 230.91 implies that a *fused, lockable * disconnect is an overcurrent device. 

Since you mentioned a fused disconnect, we now have to assume it's an overcurrent device and refer back to 690.8(a) which reads: Maximum inverter input and output circuit currents are based on inverter ratings.

Read through all that and it seems to suggest that your fused d/c only needs to be rated 125% of your inverter maximum rated ampacity. In this case, 30 amp fused d/c would be sufficient.


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## Introyble (Jul 10, 2010)

skadude said:


> I'm trying to install a wind turbine to this location. I have a variety of ideas how to connect, I just want to do the cheapest, as this is for a rural school district.
> 
> Already checked current ratings on everything, and they seem good. Turbine inverter voltage is 120/240V Split Phase. I will install a fused knife-blade switch box next to existing box for the wind turbine, then buried cable to another box at turbine site. My question is, can I wire the line-side of the switch into the line-side lugs on the existing breakers? Please indicate code reference. Below is a link to some pictures of the site.
> 
> ...


You mentioned 240VAC. 690.7 (C - D) Circuits exceeding 150 V are to be accessible by qualified persons.

What is a qualified person?


Article 100 
General

Qualified Person

The definition of “Qualified Person” A person who has the skill and knowledge related to the construction and operation of the electrical equipment and its installation. This person must have received safety training on the hazards involved with electrical systems.

Intent: This term “Qualified Person(s)” was used in about 65 Code sections throughout the 1999 NEC and the revision was intended to clarify that a qualified person must have received safety training on the hazards involved with electrical systems. No longer is a person considered qualified simply by being familiar with the construction and operation of the equipment and the hazards involved. See 110.16 Flash Protection, as an example where a qualified person is required. This makes the definition in line with OSHA and NFPA 70E requirements.


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## skadude (Aug 3, 2010)

150V line-ground is what that article says. My 240V is center-tap grounded, therefore no line-ground rating is above 120V.

But, safety is definitely an issue, especially in these school environments where I install these turbines. I always recommend that the schools install padlocks on any equipment where kids can get to them to try to prevent any issues.

I guess I'm not a "qualified person" because I don't have a piece of paper stating I sat through a NFPA training event. I would hope my MS and EIT status in Electrical Engineering says I understand something about electrical hazards, but it usually doesn't to the powers at be.


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## kub (May 27, 2009)

MDShunk said:


> Not necessarily. Every utility does it different. If they're buying it back at rate, some will just let you run the present meter backwards.


The poco here requires a second meter.


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## kub (May 27, 2009)

skadude just outta curiosity how do you bond your turbines? Every town around here requires something different


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## skadude (Aug 3, 2010)

I always have a dedicated gounding attached to the towers. Theory is you want the turbine to be the tallest thing around, which makes it a lightning rod.

I used to use a grounding rod at the base, and either wrap the ground cable around a foundation bolt, or install a lug on the base plate of the tower. Now, I lay rebar at the bottom of the foundation and attach the ground wire to the anchor bolts inside the foundation.


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## raker.robert (Jun 25, 2010)

I have installed a couple Skystreams and I set a fused disconnect and at the bottom and went into the load side of the breaker with the turbine wires. They need OCP according to the installation instructions. Then daisy chain the disconnects and back to the main with wire rated for the load of 40 amps and Voltage drop. I have bonded the tower to the rebar in the base which was a 3' x 10' deep hole that depends on soil type. When lighting strikes all bets are off, it just took out an inverter on one of the installations.


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## kub (May 27, 2009)

we've done about 20 turbines mostly jacobs and a couple bergeys 10-20kw. Generally we drive a rod at each of the 3 legs and run 4/0 braided bare copper mechanical crimp on a double hole ring teriminal on the end , drill the gussets on the bottoms of the legs and bolt it on with stainless hardware. The closest leg to the disco at thebottom of the tower the bond feeds through the rod clamp to the disco. This is what most inspectors want have had a couple want a ground ring.


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