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Grounding Shielded HV Cable
I have tried a number of searches and can't seem to find a reliable answer to my question.
I am looking at using shielded 2/0 cable to connect my motor (Edit for clarification: Tesla Drive unit battery connection not the internal 3 phase) . My assumption is that the shielded would get grounded to the car and not the traction B- . Can anybody confirm this?
I guess second question. Am I overthinking things using shielded cable? Tesla SDU is the motor.
I am looking at using shielded 2/0 cable to connect my motor (Edit for clarification: Tesla Drive unit battery connection not the internal 3 phase) . My assumption is that the shielded would get grounded to the car and not the traction B- . Can anybody confirm this?
I guess second question. Am I overthinking things using shielded cable? Tesla SDU is the motor.
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Tesla cabling is shielded. The point of shielding is to reduce EMI.
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i know the purpose of shielding, but it wasn't clear that you did, since you asked the question. What makes you think you need it--have you made measurements and exceeded some specification?
The Tesla wires are from the pack to the inverter, the HVDC B+ and B- , right? And the motor connections are internal to the inverter/motor, right? You didn't specify which one you were blabbing about or where they would be used. i don't need to make up posts, i'm not the noob asking for help.
The Tesla wires are from the pack to the inverter, the HVDC B+ and B- , right? And the motor connections are internal to the inverter/motor, right? You didn't specify which one you were blabbing about or where they would be used. i don't need to make up posts, i'm not the noob asking for help.
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I swear you are asking questions just to make questions/posts.
All the main HV cables on Teslas are shielded 2/0 cable. They are not twisted. This wouldn't make sense. I am not really looking for somebody's guess on grounding the shielding when your first post asked what the shielding even does.
If you want assistance, this is not the way to get it.
As kennybobby pointed out, there are two categories of high voltage cables in an EV: the DC link between the battery and motor (and other devices), and the 3-phase set between inverter and motor. Because you used the phrase "to connect my motor" the meaning was not clear and clarification would help, although I suppose that you are lumping the inverter in with the motor, and you are talking only about the DC link.
In a Tesla the 3-phase wiring does not appear to be shielded, but it is internal to aluminum drive unit cases. And yes, we understand what shielding is for - the question would be why you think shielding is needed in this particular case, because if you understand the purpose you have a better chance of understanding the design.
For your DC link connecting the shield around the B- cable to B- at both ends would make the shield completely pointless - it would simply be part of the conductor. Connecting that shield at only one end to the potentially noisy voltage source would make it an antenna. Assuming something other than complete stupidity by the designer, the shield would presumably connect to a chassis or component case ground, rather than B-.
Here's an example of shielding practices in VFD's - note that shields are connected to equipment chassis/cases and to a ground reference (in a vehicle, the chassis ground would be the equivalent):
VFD Series: How to Connect the Shield in VFD Cable
In general in EVs, the high voltage system is floating - neither B- nor B+ is connected to a chassis or case ground, and both are disconnected from everything else by contactors and service disconnects. Using either as a shield wouldn't make sense. If you look at the construction of a shielded HV single-conductor cable, the thick insulation is between the conductor and the shield, not between the shield and the outside, so the shield cannot be connected to anything which could possibly be at high voltage. If the B- could not be at high voltage, if it were not a floating point, then it wouldn't need insulation at all - just like a bare ground strap in a conventional car - but in fact it is bright orange and insulated for high voltage exactly like the B+ cable. I can't image how it could be acceptable to attach a shield to it.
Although DIY EV conversions don't appear to use cable shielding except where salvaged OEM components and connections are used, HV cable shielding does appear to the preferred practice. It would make sense to me to implement the Tesla's wiring and shielding design when using Tesla components.
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I felt by specifying the use of a Tesla small drive unit in my original post it was self apparent I was referring to the traction pack connection and not the internal inverter/motor one.
My question is specifically related to the fact that the batteries are not connected to chassis ground so when shielding the HV system do you ground the shielding to the battery ground or chassis one.
And in low voltage systems the shielding is really no different in that it is isolated from the conductor it is shielding. My main issue just comes to where to ground HV shielding to. Really doesn't even matter what it is connecting. In a system with two different isolated circuits. In this case a High and low voltage one. Does the shielding of the HV get connected to the chassis ground or the HV ground.
What bugged me about kenny's questions is they were more aimed at semantics than answering a real question or providing information like your reply.
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Ultimately my question could be rephrased as this. When using shielded cable as part of a HV system in an EV build is the shielded grounded to the HV Ground or the chassis ground.
Even reading papers on the subject things like single point vs multipoint are hotly debated. But most accessible information is more related to industrial installations where for safety everything is connected to Earth regardless of origin.
Even reading papers on the subject things like single point vs multipoint are hotly debated. But most accessible information is more related to industrial installations where for safety everything is connected to Earth regardless of origin.
Do you have access to a working Tesla, or can you call someone like Rich Rebuilds Ev garage to find out how Tesla connects their shields? Maybe they don't connect them to anything and
just the shield to reduce emissions. Were the cables intact on your SDU? Can you see where the shield was or wasn't connected?
As a guess, I wouldn't be surprised if the shields was just left floating. Could be wrong. So far, what I've seen from Tesla seems like they have a reason for doing things. Someone with a wide band spectrum analyzer could compare shielded cable vs. non-shielded cable on the cables from the inverter to the motor (where I would expect the most noise).
Perhaps, but not really, as some people using Tesla drive units separate the motor and inverter for packaging reasons, and then need to fabricate longer 3-phase cables.
I think the confusion starts when you create the concept of a "battery ground". That makes sense in a typical automotive 12 volt system, but not in a high voltage EV battery.
Right... it wouldn't really be a shield if it were connected to the single conductor that it is shielding, but shielded low voltage connections are normally multi-conductor cables, and in them (unlike in the HV system) one conductor is likely bonded to a chassis ground somewhere. And again, there is a high voltage negative, but not a high voltage ground.
I agree. The VFD example that I posted was the most relevant that I found in a few minutes of searching; it has all shields connected to the component cases and to earth.
Cables and connectors for EV applications clearly come in both shielded and unshielded versions, but in the specs and notes that I found I didn't see a description of what the shield should be connected to. I did notice that connectors which are secured by bolts to the component housing typically have metal-lined holes for the securing screws, suggesting that those screws electrically connect the shield to the housing, which would be an equipment or chassis ground isolated from both sides of the high voltage system. If you have the Tesla drive unit on hand, with a mating connector, that could be checked.
But those cables are within the gearbox housing, and thus shielded by the housing.
"HV Ground" is a bit of a misnomer. In a traction battery you have a positive and negative high voltage connection that are isolated from the rest of the vehicle's electronics as brian_ stated. For the cable shielding to be effective it needs to be connected to chassis ground because the chassis is (or should be) the ground reference for all of the other electronics on the vehicle. You want it tied directly to the biggest ground you have available (the chassis), so any noise has the lowest-impedance path to ground possible.
Good point! I was thinking something like a Nissan Leaf inverter separated from its motor (or the earlier version where they were separate). Then we could learn about the general case of noise and shielding. Same with a Tesla were someone and separated to the two components. Ideally on a motor dyno to see how load and noise are correlated.
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I think this gives a hint to correct grounding thinking about it as the housing is grounded to the chassis through a heavy strap.
Sadly don't have access and my cables were included but cut off at the junction box and without destroying the connector on the sdu end I cant see a way to see what they have done. Plus side I have 18 ft of shielded 2/0 cable downside no idea how it is connected. I have pdfs of all of tesla's wiring for the 12volt side of things but they make no mention to the HV side.
Pics may make this clearer to me. Can you use an ohm meter to connect to the cut-off cable shield and see what the shield is connected too? Or make some friends with tesla owners and poke around, Or find more used stuff not quite so disassembled.. Best of luck.
Bill
But you can...
My guess is that you'll find that the shield (accessible where the cable is cut) is connected to a mounting screw of the connector body, although that connection could be only at the missing end. I'm sure that you'll find that it is not connected to either HV conductor (at the cut-off point or the corresponding connector pin).
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Not with what I have. I have 2 10 ft lengths of clean cut cable and the plugs that go into the inverter with about a foot and a half of cabling attached. The yard just cleaved all the connectors off and not willing to risk destroying the connectors that go into the inverter as I have yet to identify exactly what they are. In other areas wreckers may have teslas one can go look at but here there simply aren't and that is if the yard will even let you in. As it is to find a motor I had to buy from the US
I don't think you understand what we are suggesting. That plug and attached foot and a half of cabling, unplugged from the inverter, is all that you need.
Unfortunately cutting cables is typical salvage yard practice (with any vehicle, EV or not): it's the fast way to break down a vehicle, and the assumption is that used intact cable assemblies don't have enough retail value to justify the cost of removing them intact and putting them in inventory. You would have to request them before the car was stripped to have any chance of getting a long cable in intact form.
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