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Boat Dock Exposure Voltage Mitigation
Working Group on Voltages at Publicly and Privately Accessible Locations (P1695)
January 2013January 2013
Frank Lambert and Shashi PatelFrank Lambert and Shashi PatelGeorgia Tech / NEETRAC
Problem StatementSwimming or working in the water around docks with customer owned electrical circuits and equipment installed in accordance with current applicable standards can be unsafe because the water around a dock can be at a different potential than the dock for a variety of reasons.
Proposed SolutionProposed Solution• Create a new separately
derived source that is ground isolated to feed the dock’sisolated to feed the dock s loads.
• The secondary side ground would be bonded to dock equipment as it normally would but this ground wouldwould, but this ground would have no reference to the distribution system neutral.
• This would reduce or eliminate the neutral to water voltage at docks.
Dock Isolation Unit
vo age a doc s.
Test Site 1• Permanent isolation transformer installation.• Only tested with transformer secondary grounded. • NEV hazard was mitigated by use of the isolation transformerg y• Contact voltage hazard was also mitigated
NEV Measurements
Without Iso Tx With Iso Tx
Loc Vexp‐oc Vexp‐cc* Vexp‐oc Vexp‐cc*
Fr‐W1 11.9 9.8 1.3 1.0
Fr‐W3 16.1 13.1 1.7 1.3
Deck‐W3 15.8 3.6 1.7 0.6
*Closed circuit voltage is same as exposure current*Closed circuit voltage is same as exposure current
Isolation Tx had ground on secondary
All measurements in Volts (V)
Circuit Configuration
5
Test Site 2• Test site with lowest NEV measured (under 10V).• Tested with transformer secondary grounded and floating• NEV hazard was mitigated by use of the isolation transformerg y• Contact voltage hazard was also mitigated
NEV Measurements
Wi h I T Wi h I T 2Without Iso Tx With Iso Tx2
Loc Vexp‐oc Vexp‐cc1 Vexp‐oc Vexp‐cc1
Fr‐W1 3.6 3.0 0.7/0.1 0.6/0.1
Fr‐W4 5.0 4.3 0.8/0.7 0.7/0.5
Light 2‐W 4.7 2.5 0.8/0.1 0.4/0.31 Closed circuit voltage = exposure currentClosed circuit voltage exposure current2 For Iso Tx readings: (with secondary grounded/with secondary floating)
All measurements in Volts (V)All measurements in Volts (V)
Circuit Configurationg
7
Test Site 3T ti f d t dditi l it h th hi h t NEV• Testing was performed at an additional site where the highest NEV measured was over 50V.
• NEV hazard was mitigated by use of the isolation transformer• Contact voltage hazard was also mitigated
NEV Measurements
Without Iso Tx With Iso Tx
Loc Vexp‐oc Vexp‐cc* Vexp‐oc Vexp‐cc*
Fr‐W1 19.7 15.2 0.6 0.6
Fr‐W2 22.5 17.6 1.0 0.6
Deck‐W1 20.3 5.5 0.8 0.7
*Closed circuit voltage exposure current*Closed circuit voltage = exposure current
All measurements in Volts (V)
Neutral Exposure Voltage Magnitude at Site 3
Approximately 48 VoltsApproximately 48 Volts
NEV is related to running of a local pump storage hydro plant
9
Boat Dock Testing at Site 3g
Stray Voltage Testing – Open Circuit Voltage
20
25
)
Isolation Transformer BypassedIsolation Transformer In with Secondary Grounded
15
20
tage (V
olts) Isolation Transformer In with Secondary Grounded
Isolation Transformer In with Secondary Lifted/Floating
10
Circuit V
olt
5Ope
n C
0Site 1 Low Reading*
Site 1 High Reading*
Site 2 Low Reading
Site 2 High Reading
Site 3 Low Reading
Site 3 High Reading
11
g g g g g g
*Configuration not tested
Stray Voltage Testing – Closed Circuit Voltage
20
25
Isolation Transformer Bypassed
15
20
tage (V
olts)
ent (mA)
Isolation Transformer In with Secondary GroundedIsolation Transformer In with Secondary Lifted/Floating
10
d Circuit V
olt
posure Curre
5Closed Exp
0Site 1 Low Reading*
Site 1 High Reading*
Site 2 Low Reading
Site 2 High Reading
Site 3 Low Reading
Site 3 High Reading
12*Configuration not tested
Contact Voltage Testing – Open Circuit Voltage
40
45Isolation Transformer Bypassed
30
35
age (Volts) Isolation Transformer In with
Secondary GroundedIsolation Transformer In with Secondary Lifted/Floating
15
20
25
Circuit V
olta
*Configuration not tested; results would have been similar to sites 1 and 2.
5
10
15
Ope
n
0
5
Site 1 Low Reading
Site 1 High Reading
Site 2 Low Reading
Site 2 High Reading
Site 3 Low Reading*
Site 3 High Reading*
13
Reading Reading Reading Reading Reading Reading
Contact Voltage Testing – Closed Circuit Voltage
40
45Isolation Transformer Bypassed
25
30
35
age (Volts)
nt (m
A)
Isolation Transformer In with Secondary GroundedIsolation Transformer In with Secondary Lifted/Floating
15
20
25
sed Circuit V
olta
Expo
sure Curren
*Configuration not tested; results would have been
5
10
15
Clos E esu ts ou d a e bee
similar to sites 1 and 2.
0Site 1 Low Reading
Site 1 High Reading
Site 2 Low Reading
Site 2 High Reading
Site 3 Low Reading*
Site 3 High Reading*
14
g g g g g g
NEC Change ProposalS b i d Ch f• Submitted Changes for:– Article 555 – Marinas and Boatyards (Code Panel 19) – Article 682 – Natural and Artificial Made Bodies of– Article 682 – Natural and Artificial Made Bodies of Water (Code Panel 17)
• Change Proposal Process (dates for NEC‐2014):
ropo
sal
Perio
d Change Proposal Submission
Code Panel Report on Proposal (ROP) MeetingPanel 17: 1/19‐21/2012
Code Panel (ROP) Final Ballot Results
ntPr P (by 11/4/2011)
Panel 17: 1/19 21/2012Panel 19: 1/9‐14/2012 3/9/2012
Code Panel Report on
Commen
Perio
d Comment Submission
(by 10/17/2012)
Code Panel Report on Comments (ROC) MeetingPanel 17: 12/3‐5/2012Panel 19: 12/6‐8/2012
Code Panel (ROP) Final Ballot Results
3/22/2013
Change Proposal Language (555.16)555.16 Mitigation of Neutral Related Stray Voltages and CurrentsTo provide protection for neutral related stray voltages and currents, a suitably rated
isolation transformer (a separately derived system) at the branch circuit service panel supplying the shore power shall be permittedpanel supplying the shore power shall be permitted.
The following configuration is recommended for the isolated system:(1) The isolation transformer shall have overcurrent protection on the supply side as
required in 450 3required in 450.3.(2) The isolation transformer shall be provided with a ground fault protection device
on the load side.(3) Metal enclosure of the transformer shall be connected to the supply side neutral(3) Metal enclosure of the transformer shall be connected to the supply side neutral
and grounding system as required by 250.4 (A).(4) The load side neutral and equipment grounding conductors shall be connected
together and grounded on the secondary side of the transformer as required by 250.20(B). To provide adequate isolation, the installed grounding electrode shall be located at least 6' from the nearest grounding electrode of the supply side and shall be connected to the transformer by an insulated grounding conductor.
(5) The location of the isolation transformer shall be on the load side of the service(5) The location of the isolation transformer shall be on the load side of the service disconnecting means and shall not be below the electrical datum plane.
16
Change Proposal Language (682.16)g p g g ( )682.16 Mitigation of Neutral Related Stray Voltages and CurrentsTo provide protection for neutral related stray voltages and currents, a suitably rated
isolation transformer (a separately derived system) at the branch circuit service panel supplying the shore power shall be permitted.
The following configuration is recommended for the isolated system:(1) The isolation transformer shall have overcurrent protection on the supply side as
i d i 450 3required in 450.3.(2) The isolation transformer shall be provided with a ground fault protection device on
the load side.(3) Metal enclosure of the transformer shall be connected to the supply side neutral and(3) Metal enclosure of the transformer shall be connected to the supply side neutral and
grounding system as required by 250.4 (A).(4) The load side neutral and equipment grounding conductors shall be connected
together and grounded on the secondary side of the transformer as required by g g y q y250.20(B). To provide adequate isolation, the installed grounding electrode shall be located at least 6' from the nearest grounding electrode of the supply side and shall be connected to the transformer by an insulated grounding conductor.
( ) h l f h l f h ll b h l d d f h(5) The location of the isolation transformer shall be on the load side of the service disconnecting means and shall not be below the electrical datum plane.
17
Comments / Contact InfoComments / Contact Info
Frank C LambertFrank C. LambertGeorgia Tech / NEETRAC0 6 8404‐675‐[email protected]