suspended transformer

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iwire

iwire

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Staff member
Location
Massachusetts
mgookin said:
Just curious: What structural do they let you do? The racks for the equipment but not any building structural retrofit?
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Hmm, well I know that we need them to verify the roof loading and number of attachment points I am not sure beyond that.

The systems I did where flat on the roof and fastened to the structure more or less directly. No real racking.

Now the company is doing a verity of installation types but I am not involved other than going out to the job at the beginning to layout the points on the roof with a robotic total station.
 
I

Ingenieur

Senior Member
Location
Earth
iwire said:
Could be. :D

At the least not qualified to do structural design.

The PV systems we do preset this issue and when we are design build we have to hire a designer to make sure we don't overload the roof. MA allows us to do the electrical design, not the structural.
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Hanging a transformer in a location shown on a bid set that includes bldg structural is one thing
we can assume the structural engr provided for it

adding a large load to an existing structure not included in the original design is something else
 
iwire

iwire

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Staff member
Location
Massachusetts
Ingenieur said:
When a pad is needed for a genset who does it?
assume no engineer involved
owner hires contractor
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Depends, are we talking a 45kw unit or 1 MW?

Small ones won't require engineering around here unless the owner requests it. If the owner requires it it will be worked out with them as far as who is suppling the engineering services.

The last MW one I did we acted as the GC and hired all the trades needed. If I recall the pad was what the manufacturer of the genset recommended.

But you are asking specifically about jobs that do not have an engineer when the topic here is jobs that have an engineer of record already on board.


Like you I have been doing this 30 + years, I know how it works here with the projects we do. How do you think that detail I posted ended up on the prints? The installers did not put it there the designers did. And it is typical, not the design itself but the fact there will be a detail on transformer hanging if the job requires hanging transformers.

I am quite willing to accept that other areas may do things differently, maybe you should consider that as well. :)
 
W

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Ingenieur said:
1/2" wire rope, swivels both ends 10' long
x 4 each
1000 lb suspended, 3' x 3' x 3'
how much force to displace it 1' horiz?
how much does it move vert?
state force in g
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sqrt(99)=9.95, so it moves 0.05 feet, or 0.6". The force required is just 1/10 g (100 lbs), very little. Not sure what your point is.

Here's a more interesting question: what would the load do in an earthquake? The natural period is 2 * pi * sqrt (L/g) = 2 * 3.14 * sqrt (10/32) = 3.5 seconds.

For my location, the design level spectral acceleration for a period of 1s (S_D1) = 0.952g. For periods between 1 and 8 second, S_a = S_D1/T, so the design level spectral acceleration would be 0.272g. A simple estimate of the spectral displacement is given by S_d = S_a * (T / 2pi)^2, in our case this gives S_d = (0.272*32) * (3.5 / 6.28)^2 = 2.7 feet.

2.7 feet sounds like a problem.

Cheers, Wayne
 
S

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
iwire said:
In my example is 1,000 pounds hanging from wire ropes, the only thing stoping it from horizontal movement would be the conduits and conductors. :)




I must be blessed as this sort of design is always found in the prints as I posted. Perhaps engineers around here are just more proactive.
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I have to ask, are you just trying to be argumentative and difficult, or do you actually conduct your business in the way stated during this thread? I can easily see the p!$$ing contest with the Engineer that would reif you were the EC and Ingenieuer were the EE. First off, he is in PA so seismic bracing is very likely not required there. Second, my address is Florida, but I lived in the SF Bay area for 25 years, and I know a (2) simple 45 Degree mounted pieces of Strut would brace the transformer all day long if local code required seismic bracing.

Technically you are right that if asked, an Engineer should provide you with every detail under the sun. If you want to build your jobs that way, then I suspect you won't be in business very long. Or you will be only working on say, New bridges and Nuclear power plants. Your approach in this case though would likely result in your Engineer finding a home run that the wires are 102 feet long when the spec calls for #10's for any run over 100 feet.

Good luck with that. I will just build the darn rack and call it good.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Strathead said:
I have to ask, are you just trying to be argumentative and difficult, or do you actually conduct your business in the way stated during this thread?
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I do not run a business I work for a business and yes I have been truthful with my answers as far as how the business I work for operates.

It is one of the larger shops in MA and is very successful with a great deal of repeat business.

If we tried to hang a large transformer without engineering details it would most likely hold up the inspections. As I said in this area they are really cracking down on how things are hung.

30 years ago it was a free for all, we would do anything, now not so much.

I am very willing to believe your area is not like this .... yet. ;)




can easily see the p!$$ing contest with the Engineer that would reif you were the EC and Ingenieuer were the EE. First off, he is in PA so seismic bracing is very likely not required there.
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He jumped in and described how to hang it with rods, if that is beyond his qualifications he would not do that on paper.




Second, my address is Florida, but I lived in the SF Bay area for 25 years, and I know a (2) simple 45 Degree mounted pieces of Strut would brace the transformer all day long if local code required seismic bracing.
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And I believe you, but the point has been four simple rods regarless of size used to suspend a transformer on a trapezee are not going to provide any seismic bracing.

Technically you are right that if asked, an Engineer should provide you with every detail under the sun.
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But we are not talking about how I mount an outlet box, we are talking about how to suspend a transformer overhead. There is a large difference.

If you want to build your jobs that way, then I suspect you won't be in business very long.
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The company I work for has been in business since the late 80s.


Good luck with that. I will just build the darn rack and call it good.
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And if you do that here, there is a good chance the inspector will ask for the calculations showing it is good.


Again, different areas have different procedures.
 
I

Ingenieur

Senior Member
Location
Earth
wwhitney said:
sqrt(99)=9.95, so it moves 0.05 feet, or 0.6". The force required is just 1/10 g (100 lbs), very little. Not sure what your point is.

Here's a more interesting question: what would the load do in an earthquake? The natural period is 2 * pi * sqrt (L/g) = 2 * 3.14 * sqrt (10/32) = 3.5 seconds.

For my location, the design level spectral acceleration for a period of 1s (S_D1) = 0.952g. For periods between 1 and 8 second, S_a = S_D1/T, so the design level spectral acceleration would be 0.272g. A simple estimate of the spectral displacement is given by S_d = S_a * (T / 2pi)^2, in our case this gives S_d = (0.272*32) * (3.5 / 6.28)^2 = 2.7 feet.

2.7 feet sounds like a problem.

Cheers, Wayne
Click to expand...

it's not suspended by rope
 
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