- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If the metal base completely surrounds only 1 conduit it can cause problems, regardless of how far the metal is from the conduit.
The metal needs to surround all of the conduits.
MDP switch over, isolated phases
- Thread starter Tudmutt
- Start date
The metal needs to surround all of the conduits.
I thought metal surrounding the conduit is the main issue with isolated phases? This is all new to me, trying to understand this.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If you have metal surrounding each individual conduit. Like you 3" conduit through a 4" hole, inductive heating is an potential issue. If you have all the conduits go through a single metallic hole, like your open bottom, inductive heating is less of an issue.
Im following now, tomorrow ill reach out to the electrical engineer and see what his thoughts are moving forward. Thank you
- Location
- Illinois
- Occupation
- retired electrician
I thought this was about an installation where there were 3 ferrous conduits laid out A,A,A,N B,B,B,N and C,C,C,N.
I don't think the metal bottom would make much difference.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Exactly. We have an isolated phase installation with ferrous conduits. We already have the (parasitic) magnetic core. We also have a neutral conductor in each conduit, presumably 3 'parallel' conductors. So we already have at least 1 shorted turn in the parasitic transformer.
The metal bottom adds yet another problem: it shorts the conduit together so that you can have induced current in the conduit itself.
IMHO if @tedmutt were to open 3 holes for the 3 conduit so that there was no electrical connectivity between them, then the tiny amount of sheet metal forming a magnetic path would be a drop in the bucket compared to the conduit themselves. However opening 1 large hole would make the installation far more like the original 'open bottom' installation.
Given that the original installation had a known problem but worked fine for 30 years, my _preference_ would be to fix the issue completely, with my second choice trying to match the original installation, with full open bottom or large hole for all the conduit or a plastic panel supporting the conduit through the wall into the equipment. Also: nothing metallic shorting the conduit together.
feel like the best choice would be make it open at the bottom. This is new territory for me,will wait for the electrical engineer to decide what he wants done. Hopefully he comes up with an option soon, since the mdp is currently running with this setup. I appreciate everyone's input.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Most of the larger gear here in the states do not have a metal bottom, they are just open frames against concrete. Kinda strange that the op’s is metal bottom, unless this is a mezzanine with metal diamond tread flooring. Have seen that before.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
My comment was to be a general statement about open bottoms, not specifically something to be used with this incorrect installation.
The fact the neutral is not installed correctly as a parallel conductor is also a concern not addressed simply by the open bottom.
What was the reason that inline compression splices cannot be used to extend the all of the conductors to make them the same length so this becomes a proper parallel install?
Thats another idea that could make this correct.