HV Cable Ampacity

Status
Not open for further replies.

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Right, I know anybody can express opinion here, but still there has to be some quality of opinions. There is a reason that in middle east, people from India are paid 2 times less than people from other countries, and the reason is the quality of work.

Workmanship and citing code are two different things.
 

pv_n00b

Senior Member
Location
CA, USA
I don't know of any engineer doing HV circuit analysis by hand anymore, it kind of went out with the sliderule. Invest in software that does all this and more, SKM, Etap, etc..
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
At first I am not agree with you timm333. The Mr. Sahib remarks in the no.4 post may be irrelevant for this subject, but Sahib has a very interesting contributions in other threads.
Second, I don't agree the payment is the basis of high intellectual level. You know how the salary is built: 80% good relationship with the principals 10% good relationship with the Mob and 10% luck. Sometime luck [as “an open post”] may be 100%.
Third I don't think the usual American engineer is as good theoretician as in Europe. May be you don't know the British IET or German DIN-VDE or Russian very high electrical community.
I my self I am Romania from-before the Revolution. I agree the communists was an awful regime but with all the terror above a very fine theoretical engineering grew up in the superior technical institutes and Academy.
My son as an American engineer he is very good. However, I don't think theoretically he has much to do. The American engineer is more practical than other-and this may be is the secret of the success. You know all what your boss needs you to know.:weeping:
 

Ingenieur

Senior Member
Location
Earth
Nationality has nothing to do with engineering competency
quality of education and desire/innate ability of the individual
The US has world class engineering schools
stereotypes and generalizations serve no useful purpose
my school ranked in the 70's out of 2500 worldwide
my education was heavily theoretic, some practical
there are new degree types BSEET which are geared the opposite
 

Ingenieur

Senior Member
Location
Earth
As far as compensation
the way it works here in my experience
the more $$ you make the boss (quality, qty, client satisfaction, budget, etc)
the more you make
the people I've worked for care little for your 'relationship'
a douche who does the above > suck up yes men
as long as you are consideate/respectful to the client
because THEY ACTUALLY WRITE THE PAYCHECKS
 

Sahib

Senior Member
Location
India
Julius Right: The code doesn't require ampacity derating for grouping of 3 cables other than for ambient temperature. If the 3 cables are installed improperly, then the derating factor for grouping of the 3 cables also may be required which is not readily available other than through calculation as mentioned in your posts. It is not clear whether OP started the thread to carify installation quality issues. Thanks.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
I don't know of any engineer doing HV circuit analysis by hand anymore, it kind of went out with the sliderule. Invest in software that does all this and more, SKM, Etap, etc..
Out-sourced engineering sweatshops can do that, submit engineering plans without adjusting program defaults for proper Code Standards, proper ambient, or proper Metric vs Imperial measurements.

I'm having visions of exploited & unskilled labor mindlessly punching numbers into SKM or Etap terminals, frequently generating garbage. Like calling my bank for customer support, diverted to India, where I get canned responses that don't listen to my question.

The problem is unskilled-labor exploits. India just happens to speak English, which most Americans learn before other languages. I'm sure Asian & Latin America engineers have similar sweatshops low balling the cost of their skilled engineering.
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
Sahib, you are right if you are speaking about NEC tables where all was calculated for standard maximum conditions : up to 3 core cable[ what happened if I have only 2 loaded or –extremely- a single loaded core, may I increase the load? Of course not. If you compare NEC with "hand calculated" the cross section area of the conductor it could be double.
What happened with a “hand made calculation" vis-a-vis of a "very good software"-I agree with ramsy: some times you'll get garbage-but usually you don't know all the criteria and how the software is built and some times there are differences. You cannot control the robot : the robot will guide you.
For instance I am not sure the exposed cable is exposed to direct sunshine or if the underground software take into consideration the drying of the earth around the cable.
In order to facilitate a more rapid calculation you may do your software-usually using excel Visual Basic, C++ or else.
 

Sahib

Senior Member
Location
India
Sahib, you are right if you are speaking about NEC tables where all was calculated for standard maximum conditions : up to 3 core cable[ what happened if I have only 2 loaded or –extremely- a single loaded core, may I increase the load? Of course not. If you compare NEC with "hand calculated" the cross section area of the conductor it could be double.
NEC provisions for design are sometimes conservative and how they conflict with OP question?
What happened with a “hand made calculation" vis-a-vis of a "very good software"-I agree with ramsy: some times you'll get garbage-but usually you don't know all the criteria and how the software is built and some times there are differences. You cannot control the robot : the robot will guide you.
For instance I am not sure the exposed cable is exposed to direct sunshine or if the underground software take into consideration the drying of the earth around the cable.
In order to facilitate a more rapid calculation you may do your software-usually using excel Visual Basic, C++ or else.
Software increases the productivity of a professional: Repeative design works can be carrier our reliably and quickly through a software.
 

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
I agree with you. However, how could you check the results? Compare with what?
In a power plant-or power station of 300-700 MW units we have about 20000 cables per unit-5000 of them are power cables-and we have to design the cable and the routing using a sort of AutoCAD and a “hand made” software. We prepared a lot of other software on Visual Basic and excel in order to check the results.
 

Sahib

Senior Member
Location
India
I agree with you. However, how could you check the results? Compare with what?
In a power plant-or power station of 300-700 MW units we have about 20000 cables per unit-5000 of them are power cables-and we have to design the cable and the routing using a sort of AutoCAD and a “hand made” software. We prepared a lot of other software on Visual Basic and excel in order to check the results.

Iam sorry Julius Right if my post misled you. I thought I was posting only about the 3 cable ampacity problem of the OP. I did not intend to generalize to ampacity derating for many cables.
 
In my opinion the NEC does not make it easy to calculate the correct size of mv cables. For example mv cables installed underground, direct burial or installed in ducts. Instead the make reference to required calculations made under engineering. supervision. The Neher McGRATH referenced calculation is a very complex calculation with way far to many variables. In my opinion the best electrical equipment in the World is made in the USA under our standards. However when it comes to calculating mv cable seizes, best to look up Cable catalogs with metric cables sizes and follow the detailed design tables for cable Ampacity derating calculations. Metric cable sizes given as mm sq or. sq mm are easily converted to AWG equivalent conductor sizes. Hope this is helpful.
 

topgone

Senior Member
NEC provisions for design are sometimes conservative and how they conflict with OP question?
Software increases the productivity of a professional: Repeative design works can be carrier our reliably and quickly through a software.
It also makes people dumber! I usually check software output with dear old worksheet files I made through the years!
 
Status
Not open for further replies.
Top