Dear forum folks,
We're doing a project where 15 kV EPR with a 5-mil tape shield was specified. A vendor has submitted that cable with a 3-mil tape shield.
Does anyone have any experience with the 3-mil wrap cable to suggest we stay away from it? Any opinions and recommendations are...
Thanks dpc for the reply.
Yes the Utility contribution is suspect at 200kA. However, what they've shown me certainly has the potential. There are (5) 40kA sources in a spot-network located 20 feet from the gear.
The Utility (Con-Ed) reports 200kA for the 480 and 208 Volt sources, as in 200,000...
I'm working on a system that was originally installed in the late 60s or early 70s that has two 208V, 4000-amp Square D Power-Style switchboards with fused bolt-loc pressure switches (FBPS) as the service entrance devices. The gear is labeled: SUPPLY BUS BRACING 100kA on one piece of gear, and...
Thanks for the reply David. That's my thinking as well, but having 40 years of satisfactory performance, I think they'll be reluctant to change. .. unless I can make a strong case for it.
You've raised a couple points that warrant discussion. First and formeost, if you found a neutral/ground problem, then the Study's settings may have been appropriate, and not warrant changing. And as an earleir post states, one you change it, you own it.
But gf settings can be subjective. Many...
We are developing a design for the upgrade of a 40 year-old, 13.8 kV Emergency Power System.
The existing system consists of two (2) 3.25 MW, 13.8 kV diesel gensets. These sets energize fourteen (14) 13.8:0.48 kV substations throughout a campus-wide system. Genset operation is initiated by...
Your first choice, or the "low hanging fruit", will be larger AC across-the-line (atl) started motors with 0.8 power factor.
Beyond that, the addition of pf correction caps in any electrical system needs to pay attention to harmonics that could cause problems.
And I shouldn't even make the...
I can tell you why, based on the limited information provided.
The ground-fault trip was set to minimum.
$1.6 billion spent on the stadium, but the Power Study was value-engineered out of the project, saving them $5-10 grand!
Safe bet?
John M
I'm coordinating an electrical system where a 1600 amp breaker controls six (6) K-rated dry-type transformers.
To simplify the problem, I'll say they are all 150 kVA.
The full-load amperage on a 150 kVA xf at 480 Volts ~ 180 amps. The inrush for a K-13 transformer can be as much as 15X.
Using a...
Two comments:
1) I'm on the DE PE Law and Ethics Committee, and we would never discipline someone for not carrying a crad - if it's even listed anywhere as a requirement. As noted earlier, online registration verification outdates card carrying.
2) I just ordered a DC PE rubber stamp, and to...
Don't forget about Professional Liability Insurance.
I used to practice as a two-man engineering shop with a hefty policy as required by one of my clients, for $3,000/year. In the 10+ years that it was active, I never had any claims. And when I stopped the business, the insurance company wanted...
Smell the roses young man... My recommended steps for you:
1) Embrace the basement, because it'll never again be that simple. Fix it up. Get a pool table, etc.
2) Get into martial arts for fitness and self-confidence.
3) Get a hobby - for me it's old cars.
4) Learn to cook so you can eat the...
To David's point, absolutely, and thanks for that clarification.
If that switchgear had 50 kA of available fault current, and 25 feet of #2 AWG cable is terminated on a 100 amp breaker, the fault current is reduced to about 30 kA at the termination of the cable.
John M
.. hard to resist this topic line, but limited on my availability.
You're certainly looking at it correctly.
I've attached another hastily assembled TCC that shows a #2 cable with 100 and 110 amp SQ D breakers.
Note that the breaker with adjustable instantaneous protects - but only at the Low...
Pete,
Here's a Time-Current-Characteristic curve showing a 4000 amp main on the secondary of a 3000 kVA transformer.
The instantaneous is off, which is often done to improve selectability with downstream distribution breakers.
But you can see the 4000 amp damage curve is far to the right of the...
...and to reinforce what rafiq is stating, when you plot the time-current-characteristic of an overcurrent device, say a 100 amp circuit breaker, and include on the drawing the thermal damage (withstand) curve for the #3 CU cable that's connected to it, the situation is always such that the...
I've always done electrical design to a minimum essential level, stemming from employment in a DuPont engineering group many years ago. That philosophy would dictate using the 500s, since they meet the criteria.
But there is one area that the NEC overlooks I believe, and that's where they...
... my experience with this is that engineers (of which I'm guilty of being, but not guilty of what I'm about to write...) may specify that a system meet the criteria of 519-1992 with the MCC being the Point of Common Coupling (PCC). Which, even though 519 was not created as a design...
