We have two separate 15kV feeds running into an electrical vault. The conduits run parallel to one another but they will feed two sides of a main tie main lineup. Because of the way they came out of the source vault, they need to cross in order to land on the proper load interrupter.
We would...
I have seen a number of installs of 15kV cable with a grounded tape shield on each conductor. In all of these installs, there is not a separate ground conductor pulled through the conduit.
On a new job, the engineer is calling for a separate ground wire. Can someone point me to the relevant...
I used to work with an EE who claimed that the impedance losses from the transformer are overlooked and shouldn't be. According to him, at full load, the voltage drop is about 2/3 of the impedance percentage.
Because of this, he would always specify very low impedance transformers. I argued...
We had a fault in an ATS last week. Upon inspection, we found that a wire in one of the cabinets had burned through and arced in a few places.
This is a 12.47 kV ATS (nominal 15 kV). The wires feeding the loads are large 15 kV rated cables. There are also smaller (#4) wires that feed the...
Conventional wisdom has been that switchgear is more robust and more reliable than switchboards - and that it should be specified for critical and industrial applications.
However, I know that there have been a lot of changes in molded case equipment over the last few years and I'm wondering -...
One of my clients had a 200kW generator get back-fed from the utility, which caused the alternator to catch on fire.
They're talking about having us replace the entire generator with the same unit (it was relatively new). I'm wondering - couldn't we just put a new alternator on it?
Is it...
A facility manager I work with recently had a small APC UPS catch fire and burn up. A week before, they had an SCR on a large UPS fail.
We suspect the cause to be some sort of power quality issue on the distribution system. The issues have come up since introducing some large, non-constant DC...
For a fused disconnect at 208V, there are two sets of lugs. One side is labeled "line" and it has the disconnect portion of the switch between it and the fuse. The other is the "load" side.
I was shown an installation where the two were reversed so that the fuse is still connected to "line"...
A utility transformer at our site was brought online a few days ago and blew all three line side fuses after about 10 minutes. The transformer is a 67kV/12kV 10000 kVA unit. It was brought online unloaded and none of the secondary relays tripped.
The working theory is that either water got...
I ran across some interesting news this morning regarding some old residential structures at UC Davis. A set of 15 geodesic domes were built there by students in the 70's and have been home to students ever since.
They are fiberglass shells with foam coating. The foam is degrading, and as...
I have a few questions about Surge Suppression as it relates to Lightning Protection.
1) Is the primary purpose to protect equipment from damage or to prevent a surge from coming up a wire and starting a fire?
2) In a catenary LPS system that has surge suppression at the 12kV side (i.e. on...
We are installing a set of 208V switchgear with electronic trip breakers. We brought in a testing company to test all of the breakers, and to set the timing.
Our direction was to set the Long Time trips at 1.0 and all other settings at minimum. However, there was a misunderstanding, and the...
I am slowly trying to fill in the gaps in my electrical knowledge. Right now I'm studying 3 phase panel schedules. I understand the math and code that goes into summing up phases and load types and applying code multipliers to each load type to get total demand.
What I'm not finding a good...
I am in the planning stages of a project to replace the 480V switchgear for a process that can't tolerate much down time.
One approach we're considering is to set a temporary line-up of switchgear nearby, and move the loads to the temporary line-up while we remove and replace what's there.
The...
My electrical subcontractor is installing an R-123 chiller and would like to use PVC for the pressure relief vent line rather than steel.
The Trane manual, and ASHRAE 15 both state that PVC is acceptable as long as the correct glue is used. I don't see any exceptions in the California...
I am supporting the construction of a Catenary (overhead wire) lightning protection system over buildings that store explosive materials. The design has a grounding system made up of a buried ground loop (2' deep) with a number of 10' driven ground rods connected at certain intervals.
We've...
I'm working on a redesign/retrofit of an existing metal shop building. The structure is made up of 4 rigid frames, 40 feet wide and spaced 25 feet apart.
The roof covering is supported by longitudinal purlins at 48" o.c., covered by metal roof sheeting. The existing design uses 3/8"...
Sometimes the questions we get from homeowners just make us scratch our heads and wonder what they were thinking...
Still - they need an answer.
We got a call today that someone installed their shearwall plywood over the top of their stucco lath paper/wire and they want to know if that's...
