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.

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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 8404‐675‐1855frank.lambert@neetrac.gatech.edu