RGS Bends

[Alwayslearningelec]

I have 24 runs of 4” RGS conduit going about 40’ from a piece of equipment to an enclosure.

I think about the 3 bends I need and whether they would be field bends or pre fab elbows.

It would make a difference as using factory elbows would require cutting and threading the conduit where field bends would not.

What would determine which ones are used.

I’m thinking bending RGS of that size is not practical? If so why not?

 

[Alwayslearningelec]

BTW, would there be room on a 4000A enclosed breaker for 24 sets of 4" to land or need a box above it?
Guess a cut sheet would help but don't have.
Also, I don;t think there would all the knockouts in the breaker enclosure or maybe the vendor would fabricate it with the ko's.

 

[infinity]

Why so many sets for 4000 amps?

 

[Alwayslearningelec]

Why so many sets for 4000 amps?

Yea weird. Should be about 10 right?

 

[infinity]

Yes 10*420=4200 amps.

 

[don_resqcapt19]

I have 24 runs of 4” RGS conduit going about 40’ from a piece of equipment to an enclosure.

I think about the 3 bends I need and whether they would be field bends or pre fab elbows.

It would make a difference as using factory elbows would require cutting and threading the conduit where field bends would not.

What would determine which ones are used.

I’m thinking bending RGS of that size is not practical? If so why not?

With that many runs, I would always look at field bending, assuming that you have the required equipment.

 

[Alwayslearningelec]

With that many runs, I would always look at field bending, assuming that you have the required equipment.

Understood. Why would the quantity of runs matter?

 

[steve66]

Understood. Why would the quantity of runs matter?

I'm guessing because factory bends are expensive:

4R90 :: 4" Rigid Steel 90° Elbow :: PLATT ELECTRIC SUPPLY

4 Inch Rigid Steel 90 Degree Elbow, Cat #: 4R90, Mfr: Multiple

www.platt.com

And if you can provide a hydraulic bender, and someone to knock out 72 elbows, it will be much cheaper than $36K.

 

[Alwayslearningelec]

Yes 10*420=4200 amps.

The run is 700' point to point. The engineer said it's because of voltage drop and feeder are from a generator. I used the Southwire calc. If the source is 277/480 would I input 277 or 480 into the calculator? Thanks.

Seem like 10 sets #600 would still be fine if I enter 480v.

 

[Alwayslearningelec]

Why so many sets for 4000 amps?

Exact response from engineer.

Feeders are oversized for voltage drop. The whole building is generator backed (meaning the ES board feeds the SS board). Therefore, when we look at the voltage drop downstream, we have to take into consideration normal operating conditions with utility, and generator operating conditions with generator only

 

[infinity]

Exact response from engineer.

Feeders are oversized for voltage drop. The whole building is generator backed (meaning the ES board feeds the SS board). Therefore, when we look at the voltage drop downstream, we have to take into consideration normal operating conditions with utility, and generator operating conditions with generator only

Hey it's their money. Just seems ridiculous.

 

[don_resqcapt19]

Understood. Why would the quantity of runs matter?

The set up time for the bending equipment...not worth it for a few bends, unless you need a non-standard bend.

 

[Sparkschaser]

We will field bend any time we possibly can. We have the equipment and the personnel to do it. If we don't want to send the one-shot to the job, we will bend in the shop and send it out. But that is just my 2 cents

 

[kwired]

I'm guessing because factory bends are expensive:

4R90 :: 4" Rigid Steel 90° Elbow :: PLATT ELECTRIC SUPPLY

4 Inch Rigid Steel 90 Degree Elbow, Cat #: 4R90, Mfr: Multiple

www.platt.com

And if you can provide a hydraulic bender, and someone to knock out 72 elbows, it will be much cheaper than $36K.

Seems somewhat likely you might get a better per item price if you ordered as many as OP needs, and maybe also if you ordered the conduit and other accessories needed all on same order. The price in your link is the price if any of us just randomly orders quantity of one of that item from that company.

 

[kwired]

We will field bend any time we possibly can. We have the equipment and the personnel to do it. If we don't want to send the one-shot to the job, we will bend in the shop and send it out. But that is just my 2 cents

I even have had things bent off site because I didn't have the equipment to bend it myself, usually just something that needs a minor offset or slight kick to it. Otherwise try to use factory elbows or even pull boxes in some situations to make some offset or direction change.

Finding someone that can bend 2 inch is easier than finding someone that can bend anything over 2 inch though. Somewhat same for ability of threading over 2 inch as well.

 

[electrofelon]

The run is 700' point to point. The engineer said it's because of voltage drop and feeder are from a generator. I used the Southwire calc. If the source is 277/480 would I input 277 or 480 into the calculator? Thanks.

Seem like 10 sets #600 would still be fine if I enter 480v.

Hey it's their money. Just seems ridiculous.

Yup ridiculous. The owner needs to get a second opinion, this must be one of these engineers that gets off seeing how much of their client's money they can spend. He's using the full 4,000 amps and 1.5% VD apparently. I would probably use half of the breaker rating and for something like a generator that is only occasional to used I would easily bump that up to like 5% VD.

 

[kwired]

Yup ridiculous. The owner needs to get a second opinion, this must be one of these engineers that gets off seeing how much of their client's money they can spend. He's using the full 4,000 amps and 1.5% VD apparently. I would probably use half of the breaker rating and for something like a generator that is only occasional to used I would easily bump that up to like 5% VD.

We don't know what the load is or how much VD is acceptable either though. Although source impedance is potentially a bigger issue when it comes to VD when using an on site generator vs utility for the source.

 

[synchro]

I have 24 runs of 4” RGS conduit going about 40’ from a piece of equipment to an enclosure.

Why so many sets for 4000 amps?

The run is 700' point to point. The engineer said it's because of voltage drop and feeder are from a generator.

If the voltage drop on the feeder from a generator is the main issue, does the voltage regulator in the generator have an option for "line drop compensation"? And if so, is this already being considered in the design?
This compensation approach senses the generator output current with a current transformer, and it increases the voltage by the amount that the feeder resistance would drop at that amount of current, therefore effectively cancelling the drop. This essentially creates a negative output resistance, but it has a small magnitude compared to the load impedance and so no instability results.

An alternative would be a remote sense by the generator voltage regulator at the end of the feeder so that it adjusts the excitation to keep the voltage constant at that point. This is a commonly used method with various power supplies, but I'm not aware of it being commonly used in power distribution applications.

Of course, neither of the approaches above will reduce the power lost from a feeder's resistance. And a generator will have a limited voltage control range. But if holding the voltage variation under load within a tight range is the primary driver for choosing conductor sizes, then such voltage regulation approaches could helpful.