METALS-Copper slips for 3rd day, caution ahead of Jackson Hole

* Investors not optimistic ahead of possible US stimulus
* Tin falls 3 pct after Timah resumes spot sales
* Coming Up: U.S. pending home sales, 1400 GMT

By Carrie Ho
SHANGHAI, Aug 29 (Reuters) - Copper edged lower for a third
session on Wednesday as concern about the outlook for global
demand persisted despite the possibility that the U.S. central
bank may announce measures to stimulate economic growth at a
meeting this week.
U.S. Federal Reserve Chairman Ben Bernanke will meet with
other central bankers from around the world at Jackson Hole,
Wyoming, on Friday, and is expected to detail steps to revive
the world's largest economy.
Hopes of stimulus measures have boosted gold prices, with
bullion staying near 4-1/2-month highs, but copper investors
were less convinced.
"Sentiment is bearish, with some people questioning the
effectiveness of stimulus measures by the U.S. even if they do
manage to roll out such measures this week," said Orient Futures
derivatives director Andy Du.
Three-month copper on the London Metal Exchange
dropped 0.5 percent to $7,568 per tonne by 0711 GMT.
The most active December copper contract on the Shanghai
Futures Exchange slipped 0.5 percent to close at 55,210
yuan ($8,700) per tonne.
Sentiment during the session was also dragged down by the
Shanghai stock market, which logged its lowest close
since February 2009, said CIFCO Futures analyst Zhou Jie.
Traders said losses in Shanghai copper were limited by
increased buying in the physical markets as shown in the prompt
September contract trading at a premium to forward
months .
"Traders have put more copper into ShFE warehouses to try to
take advantage of Shanghai copper's forward curve
backwardation," said a Shanghai-based physical trader.
Copper stocks on warehouses monitored by the Shanghai
Futures Exchange rose by nearly 3,000 tonnes to 158,938 tonnes
last week.
LME tin was the biggest loser of the day, dropping
2.9 percent at one point to a session low of 20,100 after
Indonesian tin producer PT Timah said it has
re-started spot sales following a three-week stoppage.

Prices had shot up 13 percent last week on news that over 90
percent of Indonesian tin miners have stopped production.

Base metals prices at 0711 GMT
Metal Last Change Pct Move YTD pct chg
LME Cu 7568.00 -39.50 -0.52 -0.42
SHFE CU FUT DEC2 55210 -260 -0.47 -0.75
LME Alum 1903.00 -13.00 -0.68 -5.79
SHFE AL FUT DEC2 15405 25 +0.16 -2.75
HG COPPER SEP2 344.00 -2.25 -0.65 0.12
LME Zinc 1860.00 -12.00 -0.64 0.81
SHFE ZN FUT DEC2 14770 35 +0.24 -0.17
LME Nickel 16175.00 -75.00 -0.46 -13.55
LME Lead 1970.75 -4.25 -0.22 -3.16
SHFE PB FUT 15170 70 +0.46 -0.78
LME Tin 20300.00 -400.00 -1.93 5.73
LME/Shanghai arb 994

Shanghai and COMEX contracts show most active months
^ LME 3-m copper in yuan, including 17 pct VAT, minus SHFE
third month