DC 48v Safety Equipments

Thread Starter

meowsoft

Joined Feb 27, 2021
367
What is good equipment for DC safety ?, is schneider EZC MCCB at main incoming (multiple incoming) and schneider acti9 MCB at branch outgoing is good ?, also fuse at load point and NH fuse at incoming for backed up MCCB is good ?, what's another equipment I needs for DC 48v application in MDP ?, Is I need negative output to earthed-grounded ?, what's good ATS for this multiple power sources ?
4 incoming, @48v 60a, solar panel, wind turbines, battery, power supply
8 outgoing branch circuit
 

Ian0

Joined Aug 7, 2020
2,252
Connect neither side to ground. Use double-pole isolators.
Use fuses rather than circuit breakers.
For any low voltage application, calculate the prospective fault current based on cable length and size, and make sure it will clear the fuses.
 

andrewmm

Joined Feb 25, 2011
1,474
What is good equipment for DC safety ?, is schneider EZC MCCB at main incoming (multiple incoming) and schneider acti9 MCB at branch outgoing is good ?, also fuse at load point and NH fuse at incoming for backed up MCCB is good ?, what's another equipment I needs for DC 48v application in MDP ?, Is I need negative output to earthed-grounded ?, what's good ATS for this multiple power sources ?
4 incoming, @48v 60a, solar panel, wind turbines, battery, power supply
8 outgoing branch circuit
could you draw us a sketch of the proposed system please to help us understand the question in a bit more detail
 

LowQCab

Joined Nov 6, 2012
558
AC vs DC Circuit Interruption ..........

When there is an excess Current, for any reason, AC or DC, the Current must be
"interrupted", (stopped), before excessive damage can occur.

When interrupting, AC or DC, current, a "PLASMA-ARC" is created ...........
In an AC Circuit, as soon as the Voltage crosses "zero-Volts",
the Plasma-Arc will stop, and will not re-form it's self.
In a DC Circuit, THE VOLTAGE NEVER GOES TO ZERO, and the Plasma-Arc will NOT STOP.

Fuses for AC-Current and DC-Current, generally operate on a similar principle, BUT,
DC-rated Fuses have a "Second-Function",
which is to EXTINGUISH and BLOCK the Plasma-Arc
which will be created when the Fuse "Blows" from excessive Current.

The Voltage-Rating of DC-Fuses IS CRITICAL !!!!
As the DC-Voltage increases, the length of the created Plasma-Arc increases.

As a rough estimate,
the Fuse for a DC Circuit usually be
about ~1.5-inches long, (~40mm), or more, for every ~100-Volts that it is rated for.
So, a ~600V rated DC-Fuse will be, at least, ~9-inches long, (~230mm), and will contain
chemicals that melt into a solid, insulating mass, under exposure to high temperatures.
These chemicals are designed to BLOCK and EXTINGUISH the created Plasma-Arc.

AC-rated Fuses usually do NOT contain these Plasma-Arc-Blocking-Chemicals,
and therefore should NEVER be substituted for DC-rated Fuses.

High-Voltage / High-Current DC Power
is much more dangerous than AC-Voltage for this reason.
.
.
.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
AC vs DC Circuit Interruption ..........

When there is an excess Current, for any reason, AC or DC, the Current must be
"interrupted", (stopped), before excessive damage can occur.

When interrupting, AC or DC, current, a "PLASMA-ARC" is created ...........
In an AC Circuit, as soon as the Voltage crosses "zero-Volts",
the Plasma-Arc will stop, and will not re-form it's self.
In a DC Circuit, THE VOLTAGE NEVER GOES TO ZERO, and the Plasma-Arc will NOT STOP.

Fuses for AC-Current and DC-Current, generally operate on a similar principle, BUT,
DC-rated Fuses have a "Second-Function",
which is to EXTINGUISH and BLOCK the Plasma-Arc
which will be created when the Fuse "Blows" from excessive Current.

The Voltage-Rating of DC-Fuses IS CRITICAL !!!!
As the DC-Voltage increases, the length of the created Plasma-Arc increases.

As a rough estimate,
the Fuse for a DC Circuit usually be
about ~1.5-inches long, (~40mm), or more, for every ~100-Volts that it is rated for.
So, a ~600V rated DC-Fuse will be, at least, ~9-inches long, (~230mm), and will contain
chemicals that melt into a solid, insulating mass, under exposure to high temperatures.
These chemicals are designed to BLOCK and EXTINGUISH the created Plasma-Arc.

AC-rated Fuses usually do NOT contain these Plasma-Arc-Blocking-Chemicals,
and therefore should NEVER be substituted for DC-rated Fuses.

High-Voltage / High-Current DC Power
is much more dangerous than AC-Voltage for this reason.
.
.
.
1. Do you think MCCB for dual current (AC and DC) is good ?, EZC100F3100 (100a 3 pole) is have 2.5kA ics breaking capacity for 125v DC

2. It is also good idea to use contactor for automatic transfer switch ?, Schneider data sheet allows DC current for AC contactor, for LC1D80M7 is about 100a for DC-2, 48-75v DC

3. It is good for using AC fuse at load point ?, step down module, ~3.8a at 48v and ~16a at 12v, it is good for protect that with 600v AC fuse in both incoming (48v) and outgoing (12v) ?

4. Do you think neutral at output side needs to be grounded-earthed for safety ?

5. Also, it is DC MCB with recloser is good ?, and acti9 schneider MCB that can works for DC is more reliable ?

Notes :
Load is have 775 motor, and stepper motor (CNC machines, 3D printer, Laser Cut, 775 motor drill machine, ...)
For point 2 it is for switching between power supply, and MPPT
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
1. Do you think MCCB for dual current (AC and DC) is good ?, EZC100F3100 (100a 3 pole) is have 2.5kA ics breaking capacity for 125v DC

2. It is also good idea to use contactor for automatic transfer switch ?, Schneider data sheet allows DC current for AC contactor, for LC1D80M7 is about 100a for DC-2, 48-75v DC

3. It is good for using AC fuse at load point ?, step down module, ~3.8a at 48v and ~16a at 12v, it is good for protect that with 600v AC fuse in both incoming (48v) and outgoing (12v) ?

4. Do you think neutral at output side needs to be grounded-earthed for safety ?

5. Also, it is DC MCB with recloser is good ?, and acti9 schneider MCB that can works for DC is more reliable ?

Notes :
Load is have 775 motor, and stepper motor (CNC machines, 3D printer, Laser Cut, 775 motor drill machine, ...)
For point 2 it is for switching between power supply, and MPPT
Stepper motor is nema 23
 

MisterBill2

Joined Jan 23, 2018
8,781
Good question about the safety of 48 volts. It is quite a bit less of a shock hazard than 120 or 220 volts, but not a zero shack hazard. The posted threshold is considered to be 30 volts, as I recall.
If your source of 48 volts is not at all grounded, then grounding one side or the other greatly increases the shock hazard because it makes ground another contact point for completing a circuit when contacting one of the conductors.
 

Ian0

Joined Aug 7, 2020
2,252
A lot of battery systems require earth leakage monitoring to determine if one side has become shorted to earth (which will not otherwise be a fault) because that would mean that a potential shock hazard was present.
Unfortunately, it's almost impossible to measure earth fault current, without introducing a connection to earth to complete the detection circuit.

60 Volts DC is deemed the highest possible Safety Extra Low Voltage, perhaps not due to shock hazard, but more than likely because hundred of millions of telephone wires would have become a "shock hazard" if the threshold had been set any lower.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
Good question about the safety of 48 volts. It is quite a bit less of a shock hazard than 120 or 220 volts, but not a zero shack hazard. The posted threshold is considered to be 30 volts, as I recall.
If your source of 48 volts is not at all grounded, then grounding one side or the other greatly increases the shock hazard because it makes ground another contact point for completing a circuit when contacting one of the conductors.
Nice idea... thanks
 

MaxHeadRoom

Joined Jul 18, 2013
23,123
60 Volts DC is deemed the highest possible Safety Extra Low Voltage, perhaps not due to shock hazard, but more than likely because hundred of millions of telephone wires would have become a "shock hazard" if the threshold had been set any lower.
Yes, 60 volts is capable of delivering a small shock, but is not considered a health hazard or dangerous.
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
A lot of battery systems require earth leakage monitoring to determine if one side has become shorted to earth (which will not otherwise be a fault) because that would mean that a potential shock hazard was present.
Unfortunately, it's almost impossible to measure earth fault current, without introducing a connection to earth to complete the detection circuit.

60 Volts DC is deemed the highest possible Safety Extra Low Voltage, perhaps not due to shock hazard, but more than likely because hundred of millions of telephone wires would have become a "shock hazard" if the threshold had been set any lower.
Why if telephone use 72v DC ? It is can shock your ear ? :)
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
Connect neither side to ground. Use double-pole isolators.
Use fuses rather than circuit breakers.
For any low voltage application, calculate the prospective fault current based on cable length and size, and make sure it will clear the fuses.
Yes... cable size and length need to be used properly, I was try use 14a wire with 40a DC, that 40a fuse isn't blown, until I changed it with 55a wire
Do you think acti9 MCB is good ?, schneider say it's have 20kA breaking capacity
Also yes... I use 3x40 busbar with double isolator also busbar was separated by 8mm acryllic
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
Yes... cable size and length need to be used properly, I was try use 14a wire with 40a DC, that 40a fuse isn't blown, until I changed it with 55a wire
Do you think acti9 MCB is good ?, schneider say it's have 20kA breaking capacity
Also yes... I use 3x40 busbar with double isolator also busbar was separated by 8mm acryllic
DC MDP panel body is grounded, with 50mm2 BC connected to AC MDP earth busbar
 

Thread Starter

meowsoft

Joined Feb 27, 2021
367
Yes... cable size and length need to be used properly, I was try use 14a wire with 40a DC, that 40a fuse isn't blown, until I changed it with 55a wire
Do you think acti9 MCB is good ?, schneider say it's have 20kA breaking capacity
Also yes... I use 3x40 busbar with double isolator also busbar was separated by 8mm acryllic
Is that seems to be good idea @LowQCab ?
 

LowQCab

Joined Nov 6, 2012
558
Please do not ask for my advice.
I do not want to be responsible for the extremely dangerous things
that you may be attempting to do without proper education, and extensive experience.

If you are going to do these things anyway, here are my small pieces of advice .........

1) Always use wire with insulation rated for at least ~600-Volts.
(this is standard practice in the USA).

2) Over-Current-Devices, ( Circuit-Breakers or Fuses ) ..........
Fuses or Circuit-Breakers must always be smaller than
the Maximum-Current-Rating of the Wire attached to them.
For Dedicated-Loads, such as a Single individual Machine or Motor,
the Circuit-Breaker or Fuse may be smaller than
the Maximum-Current-Rating of the Wire, but never larger.

3) Motors should always have a dedicated "Motor-Starter" Contactor or Relay-Box,
that is designed and sized specifically for protecting
one individual Motor from Over-Loads or excessive Heating of the Motor-Windings

4) Always use Circuit-Breakers, or Fuses, that are rated for at least 2-X of the DC Voltage.

5) Never mix AC-Wires, and DC-Wires, together.
AC and DC Circuits must NEVER
use the same Conduit-Pipe, or Junction-Boxes, or Circuit-Breaker-Panels or Fuse-Panels.

6) ALWAYS CLEARLY MARK and IDENTIFY ...........
Wires, Conduit-Pipes, Junction-Boxes, EVERYTHING,
whether it is AC or DC, and
which Circuit-Breaker-Panel or Fuse-Box is protecting that Circuit.

7) Never mix Wires from different Sources in the same Conduit-Pipe, or Junction-Box.

8) Never supply power to a Machine with separate Wires from different Sources of Power.

9) A Machine must be powered by AC, OR, DC, NEVER both at the same time.

10) All Wire Connections, or Wire-Splices, must be protected by a
Closed-Junction-Box that was specifically designed for the purpose of
protecting Wiring Connections and Splices.
Steel, Aluminum, or Approved-PVC-Plastic Boxes ONLY.

11) No Wires may be exposed anywhere FOR ANY REASON. No exceptions.

12) Use only Steel or PVC Conduit-Pipe, designed specifically for protecting Electrical Wiring.
NEVER use "Plumbing" Pipe or Fittings.
Use only Electrical-Conduit-Fittings designed and approved specifically for
Electrical-Conduit-Pipe.

13) Always insure that all Electrical-Conduit-Pipes have strong Supports or Clamps,
and are well protected against any possible Mechanical, Chemical, or Water damage.

14) Any Machine or Motor that may Vibrate or Move in any way,
must have its Power-Supply-Wires protected by approved Flexible-Conduit,
which will not be damaged by Vibration or small movements.
Never use solid Conduit-Pipe to connect to a Motor or Vibrating Machine.
Highly-Flexible Rubber-Insulated Cable may be used in installations where
protection of the Cable from damage can be guaranteed.

15) NO WIRE, OR CONDUIT-PIPE, MAY BE INSTALLED ON THE FLOOR OF THE BUILDING.
The only exception is when a "Raised-Floor" is installed in a "Data-Center",
and only with an Approved Raised-Floor-System .........,
Approved-Flexible-Wiring-Conduit may be installed under the "Raised-Floor".
Otherwise, all Conduit-Pipes must be mounted to the surface of an Interior-Wall, or
be mounted at least 8-Feet (~3-Meters) above the Floor of the Building.

This is NOT "everything" that you need to know.
These Rules are extremely important for Personnel-Safety, and Fire-Safety.
I sincerely hope that you do not find out the hard-way, how important these rules are.
.
.
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Mad Scientist 1 .GIF
 

MisterBill2

Joined Jan 23, 2018
8,781
I would add to the points presented in post #15 that it is very unwise to have those who do not understand what they are doing, or who are not aware of how to do the task correctly, or do not understand the hazards involved, both actual and potential, to work with electrical systems or equipment.
Electricity is usually invisible and so the hazards must be understood adequately prior to working with it.

And machines or enclosures fed from multiple power sources must allways have a warning label telling that fact so that any person opening that enclosure will know that there may be live conductors even though the local mains witch is off.
 

Irving

Joined Jan 30, 2016
1,540
What concerns me about the TS is the number of threads he/she has spawned across a vast array of subjects. Given they claim to be from Beijing, this smacks, IMHO, of being a start-up, possibly student/university, led project with little/no real-world experience. I could be wrong of course.... but I'm judging based on my experience of many unsafe (whether by accident or design) products I've seen from that part of the world (many with fake CE, FCC or TUV, etc approvals).
 

MisterBill2

Joined Jan 23, 2018
8,781
It certainly does seem that the TS is asking questions about things that a person qualified to run the project would already know. And that can lead to some very unfortunate results, if we somehow forget to mention some detail that we would always presume was understood. Of course, sometimes in the interest of making something fair, the project is given to those less qualified "because they need a chance to learn." That iis why student pilots often start out in those flight trainer simulators, where a crash means you must push the "reset button."
Unfortunately electrical power systems are not so forgiving.
 
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